Optical shutter assembly

ABSTRACT

The present invention pertains to an optical shutter comprising an photon-absorbing layer and a surface layer in a transparent state on at least one side of the photon-absorbing layer, wherein the optical shutter is characterized by the absorption of photons to change the photon-absorbing layer to an opaque state and to change the surface layer to a reflective state. The optical shutter is reversibly imageable between these transparent and reflective states. The optical shutter may comprise a metallized layer on at least one side of the photon-absorbing layer. Preferably, the optical shutter comprises an organic free radical compound, such as a salt of an aminium radical cation, in the photon-absorbing layer. Also provided are optical switch devices and optical buffers comprising such optical shutters and methods of switching an optical signal utilizing such optical shutters and switch devices.

RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.09/852,392, filed May 9, 2001 now U.S. Pat. No. 6,583,916, titled“Optical Shutter Assembly, a continuation-in-part of U.S. patentapplication Ser. No. 09/706,166, filed Nov. 3, 2000 now U.S. Pat. No.6,381,059, which claims priority to U.S. Provisional Patent ApplicationNo. 60/163,349, filed Nov. 3, 1999, both titled “Optical Shutter” toCarlson of the common assignee, the disclosures of which are fullyincorporated herein in their entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to the field of optical shuttersand switches, and particularly, pertains to optical shutters andswitches which operate in the near-infrared and/or visible wavelengthregions. More specifically, this invention pertains to optical shuttersand switches comprising a reversible transparent-to-reflective opticalshutter. This invention also pertains to methods of switching an opticalsignal from one input path to a selected one of a plurality of differentoutput paths by utilizing the optical shutters and switches of thisinvention.

BACKGROUND OF THE INVENTION

Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation. The disclosures of the publications, patents, and publishedpatent specifications referenced in this application are herebyincorporated by reference into the present disclosure to more fullydescribe the state of the art to which this invention pertains.

As the quantity and speed of data communications over fiber opticssystems rapidly increases due to the growing demand from Internet usageand other communications, improved all-optical switching systems are ofincreased interest to overcome the high cost and slow switching speedsof conventional switches. These conventional switches include, forexample, various mechanical switches, electro-optic switches, andthermo-optic switches, such as, for example, described in U.S. Pat. Nos.5,732,168 and 5,828,799, both to Donald. In particular, the increasedcomplexity and cost of switching systems which involve switching from anoptical signal to an electrical signal and then back to an opticalsignal have increased the level of interest in all-optical switches.

An all-optical switch provides switching of an optical signal from oneinput path to a selected one of a plurality of different output pathswithout any intermediate conversion of the optical signal to anelectrical signal. This is typically accomplished by applying anelectrical signal to a switchable element to cause the optical signal tobe selectively switched. These electro-optic switches are responsive tothe electrical signal to selectively switch the light of the opticalsignal from the input path to the selected one of the output paths.

A variety of approaches are known for making all-optical or hybridoptical switches, such as, for example, described in U.S. Pat. Nos.5,905,587 to Maeno, et al.; 5,923,798 to Aksyuk, et al.; 5,970,185 toBaker, et al.; 5,841,912 to Mueller-Fiedler, et al.; 5,091,984 toKobayashi, et al.; 5,406,407 to Wolff; 5,740,287 to Scalora, et al.;5,960,133 to Tomlinson; 5,539,100 to Wasielewski et al.; and 5,943,453to Hodgson.

The need for improved optical switches is increased by the use ofwavelength multiplexing which converts the optical signal in the opticalfiber into, for example, 16 signals at 16 different wavelengths in anear-infrared range of about 1540 to 1560 nm, as, for example, describedin Bell Labs Technical Journal, January-March 1999, pages 207 to 229,and references therein, by Giles et al.; and in U.S. Pat. No. 5,959,749to Danagher et al. The primary function of the optical switch is to addand/or drop optical signals from the multiple wavelengths travelingthrough the optical fiber. It would be highly desirable to have arraysof optical switches to handle the optical signals from multiplewavelengths per optical fiber and from multiple optical fibers, such asup to 100×100 or greater optical switch arrays. Also, it would be highlydesirable if the response time for the optical switch is ultrafast, suchas 1 nanosecond or less.

It would be advantageous if an all-optical switching system wereavailable which avoided the complexity and cost of hybrid electro-opticand other switching systems while increasing the speed of the switchingtimes from the millisecond range to the nanosecond or picosecond ranges.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to an optical shuttercomprising an organic free radical compound in which the free radicalcompound is characterized by forming an oxidized or reduced producthaving a change in absorption in a near-infrared wavelength region as aresult of a photo-induced electron transfer reaction of the free radicalcompound, wherein the change in absorption is reversible. In oneembodiment, the reversible change in absorption is induced by heat. Inone embodiment, the reversible change in absorption is induced byradiation selected from the group consisting of ultraviolet radiation,visible radiation, and infrared radiation; and, preferably, thereversible change in absorption is further induced by the presence ofoxygen.

In one embodiment of the optical shutter of this invention, the opticalshutter further comprises a metallized layer on at least one side of aphoton-absorbing layer comprising the free radical compound of theoptical shutter. In one embodiment, the metallized layer comprisesaluminum.

Another aspect of the present invention pertains to an optical shuttercomprising an organic free radical compound, preferably a radical cationcompound or a radical anion compound, in which the free radical compoundis characterized by forming an oxidized or a reduced product having achange in absorption in a visible and/or a near-infrared region as aresult of a photo-induced electron transfer reaction of the free radicalcompound, wherein the change in absorption is reversible. In oneembodiment, the optical shutter is utilized in an optical switch devicefor a fiber optics communications channel.

Still another aspect of this invention pertains to an optical shutterimageable by photons and having a first state of a low absorption andlow reflection at a wavelength and a second state of a high absorptionand high reflection at the wavelength, which shutter comprises aphoton-absorbing layer, wherein the photon-absorbing layer comprises anorganic free radical compound, as described herein, and thephoton-absorbing layer is characterized by absorption of the photons bythe free radical compound to form a reaction product having a change inabsorption at the wavelength and by a reverse reaction of the reactionproduct to regenerate the free radical compound; and wherein the shutteris characterized by being reversibly imageable between the first andsecond states. The unique properties of the optical shutter of thepresent invention may be utilized to prepare a wide variety of extremelycompact, picosecond speed optical devices including, but not limited to,optical switches in various arrays comprising one or more of the opticalshutters.

Another aspect of the present invention relates to an optical shutterhaving a first state of transparency and of a low reflectivity at arange of wavelengths and a second state of opacity and of a highreflectivity at the range of wavelengths, which shutter comprises aphoton-absorbing layer and a surface layer on at least one side of saidphoton-absorbing layer, wherein the photon-absorbing layer comprises anorganic free radical compound in at least one of the first and secondstates and is characterized by absorption of photons to form a reactionproduct having a change in absorption at the range of wavelengths; andwherein the shutter is characterized by being reversibly imageablebetween the first and second states. In one embodiment, the opticalshutter comprises a metallized layer on at least one side of saidphoton-absorbing layer. In one embodiment, the metallized layercomprises aluminum. In one embodiment, the absorption of photons imagesthe shutter from the first state to the second state, and preferably,wherein the reaction product is the free radical compound. In oneembodiment, the absorption of photons images the shutter from the secondstate to the first state, and preferably, wherein the reaction productis formed from the free radical compound. In one embodiment, absorptionof photons reversibly images the shutter between the first and secondstate.

In one embodiment of the optical shutter of this invention, the freeradical compound is a salt of an aminium radical cation. In a preferredembodiment, the free radical compound is a salt of atetrakis[4-(dialkylamino)phenyl]-1,4-benzenediamine radical cation. Inmore preferred embodiment, the free radical compound is a salt of aN,N-dialkyl-N′,N′-bis[4-(dialkylamino)phenyl]-1,4-benzenediamine radicalcation. In one embodiment, the free radical compound is a salt of ananthrasemiquinone radical anion.

In one embodiment of the optical shutter of the present invention, thewavelength range of photons imaging the shutter from the first state tothe second state is different from the wavelength range of photonsimaging the shutter from the second state to the first state. In oneembodiment, the range of wavelengths where the change in absorptionoccurs is from 400 to 2000 nm.

Still another aspect of this invention pertains to an optical shutterhaving a first state of transparency and of low reflectivity at a rangeof wavelengths and a second state of opacity and of high reflectivity atthe range of wavelengths, the shutter comprising a first surface layerin a transparent state, a second surface layer in a transparent state,and a photon-absorbing layer in a transparent state and interposedbetween the first and second surface layers, wherein the optical shutteris characterized by the absorption of photons to change at least one ofthe first and second surface layers to a state of high reflectivity andto change the photon-absorbing layer to a state of opacity; and whereinthe shutter is characterized by being reversibly imageable between thefirst and second states. In one embodiment, the optical shutter ischaracterized by the absorption of photons to change both of the firstand second surface layers to a state of high reflectivity. In oneembodiment, the changes in reflectivity of the first and second surfacelayers occur reversibly at the same time. In one embodiment, the opticalshutter comprises a metallized layer on at least one side of thephoton-absorbing layer. In one embodiment, the metallized layercomprises aluminum.

In one embodiment of the optical shutter of this invention, thereversible imaging from the second state to the first state occurs withno external energy. In one embodiment, the reversible imaging from thesecond state to the first state is induced by heat. In one embodiment,the reversible imaging from the second state to the first state isinduced by absorption of photons from one or more wavelength rangesselected from the group consisting of ultraviolet wavelength ranges,visible wavelength ranges, and infrared wavelength ranges.

Another aspect of the present invention pertains to an optical switchdevice comprising one or more optical input paths, two or more opticaloutput paths, and one or more optical shutters, as described herein, theone or more shutters having a first state of transparency and of lowreflectivity at a range of wavelengths and a second state of opacity andof high reflectivity at the range of wavelengths, and at least one ofthe one or more shutters comprises a photon-absorbing layer and asurface layer on at least one side of the photon-absorbing layer,wherein the photon-absorbing layer comprises an organic free radicalcompound and is characterized by absorption of photons to form areaction product having a change in absorption at the range ofwavelengths; and wherein the at least one of the one or more shutterscomprising the photon-absorbing and surface layers is characterized bybeing reversibly imageable between the first and second states; andwherein the switch device is characterized by being capable of switchingan optical signal entering the switch device from one of the one or moreinput paths to a selected one of the two or more output paths. In oneembodiment, the switch device further comprises an optical wavelengthconversion element to convert the optical signal having a firstwavelength to an optical signal of a second different wavelength. In oneembodiment, the optical wavelength conversion element comprises anorganic free radical compound as an active material for converting thewavelength of the optical signal having the first wavelength.

Still another aspect of this invention pertains to an optical switchdevice comprising one or more optical input paths, two or more opticaloutput paths, and one or more optical shutters, the one or more shuttershaving a first state of transparency and of low reflectivity at a rangeof wavelengths and a second state of opacity and of high reflectivity atthe range of wavelengths, and at least one of the one or more shutterscomprising a first surface layer in a transparent state, a secondsurface layer in a transparent state, and a photon-absorbing layer in atransparent state and interposed between the first and second surfacelayers, wherein the at least one of the one or more optical shutters, asdescribed herein, that comprise the photon-absorbing and surface layers,is characterized by absorption of photons to change at least one of thefirst and second surface layers to a state of high reflectivity and tochange the photon-absorbing layer to a state of opacity, and further ischaracterized by being reversibly imageable between the first and secondstates; and wherein the switch device is characterized by being capableof switching an optical signal entering the switch device from one ofthe one or more input paths to a selected one of the two or more outputpaths. In one embodiment, the at least one of the one or more opticalshutters comprising the photon-absorbing and surface layers comprises ametallized layer on at least one side of the photon-absorbing layer. Inone embodiment, the metallized layer comprises aluminum. In oneembodiment, the photon-absorbing layer comprises an organic free radicalcompound and is characterized by an absorption of photons to form areaction product having a change in absorption at the range ofwavelengths.

In one embodiment of the optical switch device of the present invention,optical signals in the one or more input paths and the two or moreoutput paths are bi-directional, and the switch device is characterizedby the ability to switch optical signals traveling in oppositedirections through the switch device. In one embodiment, the switchdevice comprises one or more external energy source elements to provideenergy to switch the optical shutter comprising the photon-absorbing andsurface layers, wherein the one or more external energy source elementsare selected from the group consisting of electrical current sourceelements, heating source elements, ultraviolet light source elements,visible light source elements, and infrared radiation source elements.In one embodiment, the one or more external source elements areconnected to an optical switch control circuit device that monitors thedesired timing for providing the energy and delivers a signal to the oneor more external sources of energy to provide the energy to the at leastone of the one or more optical shutters comprising the photon-absorbingand surface layers.

In one embodiment of the optical switch device of this invention, theoptical signal is traveling in free space in the one or more input pathsand in the two or more output paths immediately prior to and immediatelyafter the optical signal reaches the at least one of the one or moreoptical shutters comprising the photon-absorbing and surface layers. Inone embodiment, the switch device comprises a lens in the two or moreoutput paths to focus the optical signal. In one embodiment, the opticalsignal is traveling in a waveguide in the one or more input paths and inthe two or more output paths immediately prior to and immediately afterthe optical signal reaches the at least one of the one or more opticalshutters comprising the photon-absorbing and surface layers. In oneembodiment, the waveguide in the two or more output paths is taperedfrom a larger dimension in contact to at least one of the first andsecond surface layers to a smaller dimension at a distance from the atleast one of the first and second surface layers.

Another aspect of the present invention pertain to an optical cross-barswitch device, comprising (a) an array of optical shutters arranged in aplurality of columns and rows, each optical shutter having a first stateof transparency and of low reflectivity in a range of wavelengths and asecond state of opacity and of high reflectivity in the range ofwavelengths, the shutter comprising a first surface layer in atransparent state, a second surface layer in a transparent state, and aphoton-absorbing layer in a transparent state and interposed between thefirst and second layers, wherein the optical shutter is characterized bythe absorption of photons to change at least one of the first and secondsurface layers to a state of high reflectivity and to change thephoton-absorbing layer to a state of opacity; wherein the opticalshutter is characterized by being reversibly imageable between the firstand second states; and (b) a plurality of fiber optic ports, each fiberoptic port disposed at a respective one of the columns and rows andcapable of emitting and receiving a light beam so that when the lightbeam from a light emitting fiber optic port located at a selected one ofthe columns and rows is transmitted to a selected light receiving fiberoptic port located at a selected remaining one of the columns and rows,the optical shutter located at an intersection formed by the selectedcolumn and row is switched to change from the non-reflective state tothe reflective state to reflect the light beam from the light emittingfiber optic port to the selected light receiving fiber optic port. Inone embodiment, the switch device further comprises a plurality ofcollimator elements, each collimator element being disposed adjacent torespective ones of each fiber optic port and between each fiber opticport and the optical shutters. In one embodiment, when the opticalshutter located at the intersection formed by the selected column androw is in said second state, remaining ones of the optical shutterslocated in the selected column and row are in said first state. In oneembodiment, a plurality of light beams from a plurality of lightemitting fiber optic ports located at selected ones of the columns androws are transmitted to a plurality of selected light receiving fiberoptic ports located at selected remaining ones of the rows and columnsthrough a plurality of optical shutters located at respectiveintersections formed by the selected columns and rows in the respectivereflective states.

Still another aspect of this invention pertains to a method forswitching an optical signal from one optical input path to apredetermined one of a plurality of different optical output paths,which method comprises the steps of (a) providing a free-space opticalswitch device, comprising an optical shutter disposed between an opticalinput path and a first and second optical output paths, the opticalshutter being switchable between a transparent state in which the lightfrom the input path is transmitted through the optical shutter to thefirst output path, and a reflective state in which the light from theinput path is reflected from the optical shutter to the second outputpath; (b) inputting an optical signal into the input path; and (c)providing photons to switch the optical shutter reversibly between thetransparent state and the reflective state in order to selectivelydirect the optical signal to a predetermined one of the output paths. Inone embodiment, the optical shutter comprises a first surface layer in atransparent state, a second surface layer in a transparent state, and aphoton-absorbing layer in a transparent state and interposed between thefirst and second surface layers, wherein the optical shutter ischaracterized by the absorption of photons to change at least one of thefirst and second surface layers to a state of high reflectivity and tochange the photon-absorbing layer to a state of opacity; and wherein theoptical shutter is characterized by being reversibly imageable betweenthe first and second states. In one embodiment, the photon-absorbinglayer comprises an organic free radical compound in at least one of thefirst and second states.

Another aspect of this invention pertains to a method for switching anoptical signal from one optical input path to a predetermined one of aplurality of different optical output paths, which method comprises thesteps of (a) providing a optical switch device, comprising an opticalshutter disposed between an optical input port in a first inputwaveguide and both a first optical output port in a first waveguide anda second optical output port in a second output waveguide, the opticalshutter being switchable between a transparent state in which the lightfrom the input port is transmitted through the optical shutter to saidfirst output port, and a reflective state in which the light from theinput port is reflected from said optical shutter to said second outputport; (b) inputting an optical signal into the input port; and (c)providing photons to switch the optical shutter reversibly between thetransparent state and the reflective state in order to selectivelydirect the optical signal to a predetermined one of the output ports. Inone embodiment, the optical shutter comprises a first surface layer in atransparent state, a second surface layer in a transparent state, and aphoton-absorbing layer in a transparent state and interposed between thefirst and second surface layers, wherein the optical shutter ischaracterized by the absorption of photons to change at least one of thefirst and second surface layers to a state of high reflectivity and tochange the photon-absorbing layer to a state of opacity; and wherein theoptical shutter is characterized by being reversibly imageable betweenthe first and second states. In one embodiment, the photon-absorbinglayer comprises an organic free radical compound in at least one offirst and second states.

Still another aspect of the present invention pertains to a method forswitching an optical signal from one or more optical input paths to apredetermined one of two or more optical output paths, which methodcomprises the steps of (a) providing an optical switch device, asdescribed herein; (b) inputting an optical signal into the one or moreinput paths; and (c) providing photons to switch the optical shutterfrom the first state and the second state in order to selectively directthe optical signal to a predetermined one of the two or more outputpaths.

As will be appreciated by one of skill in the art, features of oneaspect or embodiment of the invention are also applicable to otheraspects or embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, particular arrangementsand methodologies are shown in the drawings. It should be understood,however, that the invention is not limited to the precise arrangementsshown or to the methodologies of the detailed description.

FIG. 1 shows one embodiment of an optical switch device utilizing theoptical shutters of the present invention.

FIG. 2 shows another embodiment of an optical switch device utilizingthe optical shutters of this invention and incorporating opticalcombining devices.

FIG. 3 shows a top down view of one embodiment of the optical shuttersof the present invention and utilizing waveguides to transmit theoptical signals with tapered waveguides on the optical output paths.

FIG. 4 illustrates a top down view of another embodiment of the opticalshutters of this invention and transmitting the optical signals in freespace with lenses present in the optical output paths.

FIG. 5A shows a top down view of one embodiment of the optical switchdevices and shutters of the present invention with the optical shutterin the transparent state and having fixed mirrors present to reflect theoptical signals in the direction of the optical output paths.

FIG. 5B shows a top down view of one embodiment of the optical switchdevices and shutters of the present invention with the optical shutterin the reflective state and having fixed mirrors present to reflect theoptical signals in the direction of the optical output paths.

FIG. 6 illustrates one embodiment of the optical shutters of thisinvention with a source of photons for switching the optical signalswhen a signal is provided by a optical shutter control circuit device.

FIG. 7 shows one embodiment of the optical cross-bar switch devices ofthe present invention.

FIG. 8 illustrates another embodiment of the optical switch devices ofthis invention.

FIG. 9 shows another embodiment of the optical switch devices of thepresent invention and having fixed mirrors to reflect the opticalsignals in the direction of the optical output paths.

FIG. 10 shows one embodiment of the optical shutters of the presentinvention in the reflective state with an angle of 30° between the pathsof the optical signals and the reflective surfaces of the opticalshutters.

FIG. 11 shows one embodiment of the optical shutters of the presentinvention in the reflective state with an angle of 45° between the pathsof the optical signals and the reflective surfaces of the opticalshutters.

FIG. 12 shows one embodiment of the optical shutters of the presentinvention in the reflective state with an angle of 75° between the pathsof the optical signals and the reflective surfaces of the opticalshutters.

FIG. 13 illustrates one embodiment of an optical buffer utilizing theoptical shutters of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The optical shutters and switch devices of the present invention providesuperior speed of response, such as a response time of 1000 picosecondsor less, to the incident radiation, and are particularly useful insystems where an all-optical shutter and switching mechanism isdesirable.

Organic Free Radical Compounds

The term “organic free radical compounds,” as used herein, pertains toorganic compounds which comprise at least one free unpaired electron onan atom, such as, for example, a carbon atom, a nitrogen atom, or anoxygen atom, in the ground state of the organic compound. Suitableorganic free radical compounds for the optical shutters of the presentinvention include neutral organic free radicals, salts of organic freeradical cations, and salts of organic free radical anions. For purposesof brevity, the terms “organic free radical cation”, “organic radicalcation”, and “radical cation” are used interchangeably herein. The word“cation,” as used herein, pertains to a positively charged atom in amolecule, such as, for example, a positively charged nitrogen atom.Similarly, the terms “organic free radical anion”, “organic radicalanion”, and “radical anion” are used interchangeably herein. The word“anion,” as used herein, pertains to a negatively charged atom in amolecule, such as, for example, a negatively charged oxygen atom. Itshould be noted that the free unpaired electron and the positive andnegative charges of the organic free radical compounds may be localizedon a single atom or shared among more than one atom.

Examples of suitable organic free radical cations for the opticalshutters and switch devices of this invention include, but are notlimited to, aminium radical cations, such as, for example, tris(p-dibutylaminophenyl) aminium hexafluoroantimonate, which iscommercially available as IR-99, a trademark for a dye available fromGlendale Protective Technologies, Inc., Lakeland, Fla. An equivalentchemical name for IR-99, used interchangeably herein, is thehexafluoroantimonate salt ofN,N-dibutyl-N′,N′-bis[4-dibutylamino)phenyl]-1,4-benzenediamine radicalcation. IR-99 is known to be a stable material that may exist in a layerof material, such as in a polymeric coating, under normal roomconditions for an extended period of time. Other suitable aminiumradical cations with a tris (p-dibutylaminophenyl) aminium saltmolecular structure include IR-126 and IR-165, which are trademarks fordyes available from Glendale Protective Technologies, Inc., Lakeland,Fla. These two dyes are likewise known to be stable in the dry powderform and in a layer of material, such as in a polymer-containingcoating, under ambient room conditions for extended periods of time,such as many years.

IR-126, which is the hexafluoroantimonate salt oftetrakis[4-(dibutylamino)phenyl]-1,4-benzenediamine radical cation, isparticularly preferred for use in the optical shutters and switchdevices of this invention because of its very intense and relativelyflat absorption across the 1400 to 1700 nm wavelength region typicallyutilized for optical Internet fiber optic communication channels andbecause of its one-electron reduction to a very transparent neutralnon-free radical compound which has no significant absorption above 500nm. Also, IR-126 may undergo a one-electron oxidation to IR-165, whichhas a much lower absorption in the 1500 to 1700 nm wavelength region.

Examples of suitable organic free radical anions for the opticalshutters of the present invention include, but are not limited to,anthrasemiquinone radical anions, such as, for example, described inPhotochemistry and Photobiology, Vol. 17, pages 123-131 (1973) byCarlson and Hercules.

For example, under oxidative or reductive conditions, a lightyellow-green layer comprising IR-165 upon laser exposure at 1065 nm mayundergo photo-induced electron transfer reactions which competeefficiently with the ultrafast photothermal processes of IR-165 toproduce an oxidized product having a change in absorption in both thevisible and the near-infrared wavelength regions or, alternatively, toproduce a reduced product having a change in absorption in both thevisible and the near-infrared wavelength regions. For example, theoxidized product of IR-165 may be a blue compound from a two-electronphoto-induced electron transfer reaction, particularly when the layer ofIR-165 comprises a polymer, such as nitrocellulose, which promotesoxidation of IR-165 upon exposure to radiation. Similarly, for example,the reduced product of IR-165 may be an intense green compound from anone-electron photo-induced electron transfer reaction, particularly whenthe layer of IR-165 comprises a polymer which does not promote oxidationof IR-165 upon exposure to radiation. The green, reduced product ofIR-165 has new intense absorption peaks at 950 nm and 1480 nm, incomparison to the absorption of IR-165. One of the green, reducedproducts of IR-165 is IR-126, which is an one-electron reduction productof IR-165. Depending on the other materials present in the layer, theseblue oxidized or green reduced compounds may be transient compounds andmay revert to the starting IR-165 material at various speeds from lessthan 0.1 milliseconds to many seconds. A photo-induced reaction may beutilized to accelerate the reversion back to the starting IR-165material.

Also, for example, layers comprising anthrasemiquinone radical anions,including the many possible substituted and other derivatives of theanthrasemiquinone radical anion, may undergo photo-induced electrontransfer reactions which occur very rapidly and compete efficiently withthe photothermal processes of these radical anions, to produce a reducedproduct having a change in absorption in both the visible and thenear-infrared wavelength regions. This change in absorption typicallyincludes a loss in absorption in the near-infrared wavelength region dueto the conversion of the radical anion to a non-free radical compound,such as, for example, a dianion.

Optical Shutters and Switch Devices

One aspect of the present invention pertains to an optical shuttercomprising an organic free radical compound in which the free radicalcompound is characterized by forming an oxidized or a reduced producthaving a change in absorption in a visible and/or a near-infraredwavelength region as a result of a photo-induced electron transferreaction of the free radical compound.

Another aspect of the present invention relates to an optical shutterhaving a first state of transparency and of a low reflectivity at arange of wavelengths and a second state of opacity and of a highreflectivity at the range of wavelengths, which shutter comprises aphoton-absorbing layer and a surface layer on at least one side of saidphoton-absorbing layer, wherein the photon-absorbing layer comprises anorganic free radical compound in at least one of the first and secondstates and is characterized by absorption of photons to form a reactionproduct having a change in absorption at the range of wavelengths; andwherein the shutter is characterized by being reversibly imageablebetween the first and second states.

Still another aspect of this invention pertains to an optical shutterhaving a first state of transparency and of low reflectivity at a rangeof wavelengths and a second state of opacity and of high reflectivity atthe range of wavelengths, the shutter comprising a first surface layerin a transparent state, a second surface layer in a transparent state,and a photon-absorbing layer in a transparent state and interposedbetween the first and second surface layers, wherein the optical shutteris characterized by the absorption of photons to change at least one ofthe first and second surface layers to a state of high reflectivity andto change the photon-absorbing layer to a state of opacity; and whereinthe shutter is characterized by being reversibly imageable between thefirst and second states. In one embodiment, the optical shutter ischaracterized by the absorption of photons to change both of the firstand second surface layers to a state of high reflectivity. In oneembodiment, the changes in reflectivity of the first and second surfacelayers occur reversibly at the same time. In one embodiment, the firstand second surface layers are in direct contact to the photon-absorbinglayer. In one embodiment, the at least one of the first and secondsurface layers are not in direct contact to the photon-absorbing layer.In one embodiment, the optical shutter comprises two or morephoton-absorbing layers interposed between the first and second surfacelayers. In one embodiment, the first surface layer is in direct contactto a first one of the two or more photon-absorbing layers and the secondsurface layer is in direct contact to a second one of the two or morephoto-absorbing layers. In one embodiment, the photon-absorbing layercomprises an organic free radical compound and is characterized by anabsorption of photons to form a reaction product having a change inabsorption at the range of wavelengths, and preferably, the reactionproduct is the free radical compound. In one embodiment, the absorptionof photons images the optical shutter from the second state to the firststate, and, preferably, the reaction product is formed from the freeradical compound.

The term “near-infrared wavelength region,” as used herein, pertains towavelengths from 700 nm to 2000 nm. The term “visible wavelengthregion,” as used herein, pertains to wavelengths from 400 to 700 nm. Inone embodiment, the free radical compound is a radical cation,preferably an aminium radical cation, and most preferably, the radicalcation is tris (p-dibutylaminophenyl) aminium hexafluoroantimonate(TAH). In a preferred embodiment, the free radical compound is a salt ofa tetrakis[4-(dialkylamino)phenyl]-1,4-benzenediamine radical cation,such as, for example, the hexafluoroantimonate salt oftetrakis[4-(dibutylamino)phenyl]-1,4-benzenediamine radical cation.Besides n-butyl groups, other suitable alkyl groups include any of thealkyl groups, such as, for example, methyl, ethyl, 2-propryl, n-pentyl,and n-hexyl, and combinations thereof. In one embodiment, the freeradical compound is a radical anion, preferably an anthrasemiquinone(ASQ) radical anion.

In one embodiment of the optical shutter of the present invention, theoptical shutter comprises a metallized layer on at least one side of thephoton-absorbing layer, preferably on the side through which the photonsenter the photon-absorbing layer to form the reaction product. In oneembodiment, the metallized layer comprises aluminum. The metallizedlayer is typically very transparent, such as an optical density of lessthan 0.05 at the wavelength of the states of low and high absorptions ofthe optical shutter. These low absorptions of the metallized layer maybe obtained by using extremely thin layers of the metal, such as lessthan 10 Angstroms in thickness. The metallized layer may be utilized toprovide reflectivity at the surface of the optical shutter which isreversibly increased, for example, from less than 1% reflective when theoptical shutter is in the first state of low absorption to more than 90%reflective when the optical shutter is in the second state of highabsorption, simultaneous with the imaging of photon-absorbing layer ofthe optical shutter from “transparent” to “opaque” and back to“transparent”. This provides an overall reversible switching betweentransparent and reflective states. Also, the metallized layer may beutilized to provide a heat conduction path to dissipate heat generatedduring the imaging of the optical shutter by connection to a heat sink,such as a larger volume of a metal. For example, aluminum is known toconvert absorbed photons to heat and to conduct heat to adjacent areasat speeds of about 1 picosecond.

In one embodiment, the optical shutter of this invention furthercomprises a surface layer having a low reflectivity state, such as a 45°reflectivity of less than 1% at the wavelength of the states of low andhigh absorptions, wherein the optical shutter is characterized by theabsorption of the photons by the free radical compound or by anotherphoton-absorbing compound to form a high reflectivity state, such as a45° reflectivity of more than 90% at the wavelength of the states of lowand high absorptions, of the surface layer; and wherein the opticalshutter is characterized by being reversibly imageable between the lowand high reflectivity states. Preferably, the surface layer is on theside of the photon-absorbing layer through which the photons enter to beabsorbed to form the reaction product. In one embodiment, the absorptionof the photons images the optical shutter from the first state of lowabsorption and the low reflectivity state and to the second state ofhigh absorption and the high reflectivity state. In one embodiment, theabsorption of photons images the optical shutter from the first state tothe second state, and preferably, the reaction product is the freeradical compound. In one embodiment, the absorption of photons imagesthe optical shutter from the second state to the first state, andpreferably, the reaction product is formed from the free radicalcompound. In one embodiment, the absorption of photons reversibly imagesthe optical shutter between the first and second states.

Suitable materials for the surface layer include, but are not limitedto, metals that melt at a temperature above 25° C. and below 700° C.,and preferably below 200° C. The surface layer may include an organicfree radical compound selected for efficient photon-to-heat conversionand other organic materials, such as, for example, those that undergo arapid reversible melt-solidification process that enhances thereversible speed and the percent reflectivity of the high reflectivitystate. Also, for example, the surface layer may include a thermochromiccompound, such as, for example, a vanadium (IV) oxide that reversiblychanges between a transparent state and a reflective and opaque state atabout 68° C. A metallized layer on at least one side of thephoton-absorbing layer may enhance the efficiency of the reversibleimaging.

The optical shutter of the present invention may be utilized in avariety of product applications. In one embodiment, the optical shutteris utilized in an optical switch device for a fiber opticscommunications channel.

In one embodiment of the optical shutter of the present invention, thechange in absorption is greater than 0.1, preferably greater than 0.5,and more preferably greater than 1.5, and most preferably greater than3.0. These absorption changes are measured in optical density units, asknown in the art, where an optical density of 1.0 corresponds to 90%absorption and 10% transmission of the incident wavelength orwavelengths of radiation. Thus, for example, an initial absorption oroptical density of the optical shutter of 0.1 at 1546 nm that changes toan absorption or optical density in the optical shutter of 1.6 at 1546nm would have a change in absorption of 1.6 minus 0.1 or 1.5.

In one embodiment, the range of wavelengths is from 400 to 2000 nm. Inone embodiment, the range of wavelengths is from 1000 to 1700 nm. In oneembodiment, the range of wavelengths is from 1400 to 1700 nm. In oneembodiment, the range of wavelengths is from 1500 to 1700 nm.

In one embodiment, the near-infrared wavelength region of the change inabsorption is from 700 to 1000 nm. In one embodiment, the near-infraredwavelength region of the change in absorption is from 1000 to 1400 nm,preferably from 1400 to 1600 nm, more preferably from 1520 to 1580 nm,and most preferably from 1500 to 1700 nm.

In one embodiment of the optical shutter of this invention, thephoto-induced electron transfer reaction occurs in less than 1nanosecond after absorption of photons by the free radical compound,preferably occurs in less than 0.1 nanoseconds, more preferably occursin less than 0.01 nanoseconds, and most preferably occurs in less than0.001 nanoseconds.

In one embodiment of the optical shutter of the present invention, thephoto-induced electron transfer reaction is an oxidation of the freeradical compound. Suitable electron transfer reactions include, but arenot limited to, an one-electron oxidation of the free radical compound,a two-electron oxidation of the free radical compound, an one-electronreduction of the free radical compound, and a two-electron reduction ofthe free radical compound. The oxidation product of a radical cation maybe a diradical dication which may readily undergo reverse electrontransfer to regenerate the radical cation. Also, the reduction productof a radical anion may be a dianion which may readily undergo reverseelectron transfer to regenerate the radical anion and, in the case of anASQ radical anion and the corresponding dianion, this could involve thecontrolled presence of oxygen during the reverse electron transferprocess.

In a preferred embodiment of the optical shutter of this invention, thechange in absorption is reversible. In one embodiment, the reversiblechange in absorption is induced by heat. In one embodiment, thereversible change in absorption is induced by radiation selected fromthe group consisting of ultraviolet radiation, visible radiation, andinfrared radiation; and, preferably, the reversible change in absorptionis further induced by the presence of oxygen. For example, the ASQradical anion and the corresponding dianion are both unstable in thepresence of oxygen and, in the presence of oxygen, may be oxidized tothe corresponding anthraquinone compound, which anthraquinone compoundmay subsequently be photoreduced or otherwise reduced by known methodsto form the corresponding ASQ radical anion. In one embodiment, thereversible change in absorption occurs at less than 50° C. in theabsence of radiation or any other external source of energy. In oneembodiment, the reversible change in absorption occurs in less than 1second, preferably occurs in less than 10 milliseconds, more preferablyoccurs in less than 1 millisecond, and most preferably occurs in lessthan 0.1 milliseconds.

In one embodiment, the wavelength range of the photons to form thereaction product comprises one or more ultraviolet wavelengths. In oneembodiment, the wavelength range of the photons to form the reactionproduct comprises one or more wavelengths from 400 to 700 nm. In oneembodiment, the wavelength range of the photons to form the reactionproduct comprises one or more wavelengths from 700 to 2000 nm.

In one embodiment of the optical shutter of the present invention, thephoto-induced electron transfer reaction is induced by ultravioletradiation. In one embodiment, the photo-induced electron transfer isinduced by visible radiation, and preferably is induced by near-infraredradiation. In one embodiment, the photo-induced electron transferreaction is induced by absorption of photons by a free radical groundstate of the free radical compound. This is particularly important wherethe excited states of the free radical moiety ground state of the freeradical compound can not be efficiently populated by absorption by anon-free radical ground state, such as, for example, by an aromaticmoiety ground state, and by its subsequent internal conversion to alower excited state related to the free radical moiety ground state.

In one embodiment of the optical shutter of this invention, the opticalshutter further comprises a metallized layer on at least one side of aphoton-absorbing layer comprising the free radical compound of theoptical shutter. In one embodiment, the metallized layer comprisesaluminum. This metallized layer may serve a variety of functions, suchas, for example, reflecting more incident radiation back through theoptical shutter, enhancing heat development in the optical shutter, andacting as an enhanced or a reduced reflective element in an opticalswitch device comprising the optical shutter of this invention.

Still another aspect of this invention pertains to an optical shutterimageable by photons and having a first state of a low absorption at awavelength and a second state of a high absorption at the wavelength,which shutter comprises a photon-absorbing layer, wherein thephoton-absorbing layer comprises an organic free radical compound, asdescribed herein, and the photon-absorbing layer is characterized byabsorption of the photons by the free radical compound to form areaction product having a change in absorption at the wavelength and bya reverse reaction of the reaction product to regenerate the freeradical compound; and wherein the shutter is characterized by beingreversibly imageable between the first and second states.

A wide variety of organic free radical compounds, such as variousneutral free radicals, salts of radical cations, and salts of radicalanions, may be utilized in the optical shutters of the presentinvention. Particular advantages for the use of organic free radicalcompounds in the optical shutters of this invention include, but are notlimited to, their extremely intense infrared absorptions at the desiredwavelengths for photon excitation and/or the absorption changesassociated with optical shutters; their unique ultra-high speed photonconversions at as fast as sub-picosecond times; their stability todegradation by heat, light, or ambient conditions of moisture and air;their ease of fabrication by, for example, coating or plastic molding;and their non-toxicity.

Their extremely intense absorptions are particularly beneficial inreducing the amount of material that is needed to produce the desiredreversible absorption change in the optical shutter and thereby allowthe optical shutter to be made on a very miniature scale, such as lessthan 8 microns for the thickness of the layer of the optical shutterwhich absorbs the photons and causes the absorption change. This layermay be made much thicker than 8 microns if desired in the fabrication ofthe optical shutter for use in optical switch devices and other opticalcomponents, but the amount of the organic free radical compound used maybe kept small since the thicker layers do not need to contain anyadditional organic free radical compound to maintain the desired levelof absorption changes. In one embodiment, the thickness of thephoton-absorbing layer is 0.5 to 5000 microns. In one embodiment, thethickness of the photon-absorbing layer is 2 to 100 microns. In oneembodiment, the thickness of the photon-absorbing layer is 4 to 25microns. In one embodiment, the thickness of the photon-absorbing layeris less than 8 microns.

For example, IR-165 and IR-126 are illustrative of one type of theorganic free radical compounds for the optical shutters of thisinvention and may be reversibly formed in a photon-induced one electrontransfer reaction, where IR-126 is the one-electron reduction product ofIR-165 and, conversely, IR-165 is the one-electron oxidation product ofIR-126. IR-165 has an extremely high molar extinction coefficient ofabout 80,000 liters/mole-cm at 1065 nm where photon excitation may bedone and has low molar extinction coefficients of less than about 5,000liters/mole-cm in the 1530 to 1620 nm range where optical shutters maybe utilized in optical switch devices and other optical components in afiber optics communications channel. IR-126 has a very high molarextinction coefficient of about 40,000 liters/mole-cm in a broad andrelatively flat absorption across the 1530 to 1620 nm wavelength range,as well as absorbing at about this same molar extinction coefficientdown to about 900 nm and also absorbing out to above 2000 nm.

Assuming that IR-126 is present at about a 25% loading by weight in thephoton-absorbing layer of the optical shutter and needs to have anoptical density of greater than 3.1 in order to provide greater than99.9% absorption at the wavelengths in the 1530 to 1620 nm range toobtain the contrast ratio of greater than 30 dB that is desired in anoptical shutter in a fiber optics communications channel, thephoton-absorbing layer containing IR-126 only needs to be about aminimum of 4 microns thick in the direction that the optical signaltravels. Since the optical signals are typically traveling in only oneplane of the optical shutter, the dimensions of the optical shutterperpendicularly to this plane may be significantly less or greater thanthe thickness traveled by the optical signal. For example, in the casewhere a source of photons is utilized to switch the optical shutter andis provided from a direction above and/or below the plane of the opticalshutter traveled by the optical signals, the optical density my be, forexample, only about 1.0 with a thickness of the photon-absorbing layerin that direction of about 1.3 microns when the loading of IR-126 is 25%by weight. When the loading of the compound whose absorption isswitching in the optical shutter of this invention is increased ordecreased, the dimensions of the photon-absorbing layer may becorrespondingly decreased or increased. In the case where IR-126switches by a reversible one-electron reduction to a highly transparentnon-free radical amine, the ability to achieve a contrast ratio ofgreater than about 1000 or about 30 dB is particularly enhanced.

Assuming, for example, a 25% loading of IR-126 in the photon-absorbinglayer of the optical shutter of the present invention with about a 4micron thickness of the photon-absorbing layer in the direction that theoptical signals travel and about a 1.3 micron dimension in theperpendicular directions to the optical signal path, one form for theoptical shutter would be a cylinder. The optical signals could passthrough the cylinder in the direction of the axis of the cylinder, andthe source of photons would be directed at the sides of the cylinder. Inthe optical shutters comprising a surface layer on each side of thephoton-absorbing layer in the direction that the optical signals pass,it is advantageous to keep the thickness of the photon-absorbing layerin this optical signal direction as low as possible so that lightreflected off both these surface layers in the reflective state may becollected in the optical output path with an efficiency similar to thatwhen the light of an optical signal passes through the optical shutterin its transparent state. To aid in this efficient collection, a varietyof light collection elements, such as a focusing lens for an opticalshutter in a free space configuration or as a tapered waveguide ofgreater dimensions next to the reflective surface area in a waveguideconfiguration, may be utilized with the optical shutters and switchdevices of the present invention.

Also, for example, since each optical shutter in this case would containabout 2×10⁻¹² grams of IR-126, less than 1 microgram of IR-126 would beneeded to make approximately 16,000 optical shutters, such as might beutilized in a 1200×1200 optical switch device. Also, for example, due tothe extremely small size of the optical shutters, a 1200×1200 opticalswitch device could have a volumetric size as small as 0.001 cm³ or evensmaller, although a larger size might be selected for ease offabrication and integration with the source of photons and with otheroptical components.

While not wishing to be bound by any particular theory, the uniqueultra-high speed photon conversions of the organic free radicalcompounds, such as at sub-picosecond speeds, are thought to be greatlyinfluenced by the unique free radical character of their ground statesand perhaps of their excited states. Picosecond and sub-picosecondspeeds are particularly useful for optical shutters where, for example,nanosecond optical switching of optical data packets is desired, asknown in the art of fiber optics communications channels, and, also forexample, where protection of eyes or sensors from radiation is desiredin a picosecond or faster speed.

The optical shutter of the present invention may be illustrated in oneembodiment by an optical shutter comprising a photon-absorbing layer,wherein the photon-absorbing layer comprises IR-165, an organic radicalcation. The thickness of the photon-absorbing layer is 4 microns, andthe IR-165 is present at 25 weight percent of the photon-absorbinglayer. This optical shutter is imageable by photons, such that, forexample, when IR-165 in the photon-absorbing layer absorbs photons of1065 nm wavelength and the photon-absorbing layer comprises a reductive,electron-donating matrix of polymers, counteranions, and other additivesaround the aminium radical cation, IR-165 forms a reaction product, suchas an one-electron reduction product which is the same as or similar toIR-126 depending on the counteranion. Prior to the absorption ofphotons, the optical shutter has a state of low absorption, such as anoptical density of less than 0.05 due to IR-165, at a wavelength, suchas 1620 nm. After the absorption of photons and the formation of thereaction product, the optical shutter has a state of high absorption,such as an optical density of 3.1 due to IR-126 or a similar organicfree radical compound, at the wavelength, such as 1620 nm. Subsequently,by a dark reaction at ambient or room temperatures or at temperaturesless than 50° C. in the absence of radiation, the reaction product, suchas IR-126 or a similar organic free radical compound, undergoes areverse reaction to regenerate the starting free radical compound,IR-165, and to return the optical shutter to the state of low absorptionat the wavelength, such as 1620 nm.

Alternatively, the reverse reaction may be induced by heat, either byheat produced during the imaging process that raises the temperature ofthe photon-absorbing layer above 50° C. or by the external applicationof heat from a heat source, such as maintaining the optical shutter in ahot environment at a temperature greater than 50° C. The aminium radicalcations are typically stable at temperatures up to 250° C. and are knownto be stable under non-thermal equilibrium conditions, such as thoseexperienced in laser ablation imaging, at temperatures up to 600° C.

Also, alternatively, the reverse reaction may be induced by radiationselected from the group consisting of ultraviolet radiation, visibleradiation, and infrared radiation. Where the reaction product or othercomponents present in the photon-absorbing layer have oxygen-sensitivereactivities, the presence of a desired level of oxygen in combinationwith the radiation may be utilized to induce the reverse reaction. Inone embodiment, the wavelength of the radiation inducing the reversereaction is different from the wavelength of the photons absorbed toform the reaction product. In one embodiment of the optical shutters ofthis invention, the wavelength range of photons imaging the opticalshutter from the first state to the second state is different from thewavelength range of photons imaging the optical shutter from the secondstate to the first state. For example, a photosensitizer, such as ananthraquinone, an ASQ radical anion, or an anthraquinone dianion in thecase of a salt of an aminium free radical cation as the free radicalcompound that switches, may be utilized to sensitize the reversereaction where the photosensitizer has a strong absorption in thevisible region in the wavelength range of about 500 to 700 nm, where theaminium radical cations typically have a very weak absorption. In thiscase, for example, low cost laser diodes, such as those emitting at 635nm as used for DVD recording or those emitting at 680 nm as used formagneto-optic disk recording, may be utilized for one of the twodifferent photon-induced reversible switching reactions. For example, aphotosensitizer absorbing strongly at 635 nm could be utilized in aphoton-absorbing layer comprising IR-126 to cause the photon-inducedreduction to its corresponding highly transparent non-free radical amineor, alternatively, to cause the photon-induced oxidation of this amineback to IR-126. Thus, although the mechanism of the reverse reaction maybe varied, the optical shutter of this invention is characterized bybeing reversibly imageable between the first and second states ofabsorption at the wavelength.

The speed and/or timing of the reverse reaction may be varied over awide range depending on the requirements of the product application. Inone embodiment, the reverse reaction occurs in 1 second to 10 yearsafter the photo-induced formation of the reaction product. In oneembodiment, the reverse reaction occurs in less than 1 second. In oneembodiment, the reverse reaction occurs in less than 10 milliseconds. Inone embodiment, the reverse reaction occurs in less than 1 millisecond.In one embodiment, the reverse reaction occurs in less than 0.1milliseconds. In one embodiment, the reverse reaction occurs in lessthan 0.01 nanoseconds or 10 picoseconds, such as in 2 to 3 picosecondsor less. When radiation is used to induce the reverse reaction, thetiming of the reverse reaction may be selected depending on the timingof the exposure of the optical shutter to the radiation.

Also, with radiation to induce the reverse reaction, the speed may be asfast as the speeds of forming the reaction product after the absorptionof the photons, such as, for example, sub-picosecond speeds. Forexample, when a reversible photon-induced electron transfer occurs inthe optical shutter, the speed of the formation of the reaction productmay be sub-picosecond and as low as 40 femtoseconds or less and thespeed of a dark or heat-induced reverse reaction of the reaction productto regenerate the starting organic free radical may be as fast as 2 to 3picoseconds. Since the reversible electron transfer involved in theswitching of the optical shutter and switch device of this inventiondoes not require a chemical bond breaking, the speeds of the opticalswitching may be as fast as the sub-picosecond range. These fast speedsare particularly advantageous for optical shutters for use in nanosecondoptical packet switching, as known in the art of fiber opticscommunications channels.

The wavelengths of the photons absorbed by the photon-absorbing layer toform the reaction product may be selected from a wide variety ofwavelengths depending on the absorption spectra of the organic freeradical compound and the photon-absorbing layer, the wavelengthsavailable from the source of photons, and any need to avoid using awavelength that may interfere with the wavelength at which the opticalshutter has its states of low and high absorptions and is designed tooperate as an “on-off” switch. In one embodiment, the wavelength of thephotons is one or more ultraviolet wavelengths. In one embodiment, thewavelength of the photons is one or more wavelengths from 400 to 700 nm.In one embodiment, the wavelength of the photons is one or morewavelengths from 700 to 2000 nm. In a preferred embodiment, theabsorption of the photons by the free radical compound is from a freeradical ground state of the free radical compound, and more preferably,the wavelength of the photons absorbed by the free radical ground stateis one or more wavelengths from 700 to 2000 nm.

A wide variety of sources of the photons to form the reaction productand, when radiation is used to induce the reverse reaction, toregenerate the starting free radical compound, may be utilized. Suitablesources of photons include, but are not limited to, lasers, continuouslight sources such as mercury lamps, pulsed light sources such as xenonpulse lamps, and electroluminescent light-emitting diodes (LEDs), asknown in the art of high intensity sources of photons. It is preferredto provide the photons in pulses such that suitable light sourcesinclude pulsed lasers and other pulsed light sources.

Alternatively, in one embodiment, with lasers and continuous lightsources, a first modulator is interposed between the laser or thecontinuous light source to provide a desired length of imaging time anda desired imagewise area for the imaging of the optical shutter by thephotons. Suitable modulators may be any of the variety of lightmodulators, such as electro-optic modulators, known in the art of lightmodulators, depending on the requirements for the “on-off” imaging, suchas, for example, 1.5 picoseconds “on” of providing photons and 20nanoseconds “off” or, alternatively, 20 nanoseconds “on” and 1.5picoseconds “off”, of the modulator and of the desired imagewise area,such as, for example, a dot or pixel shape of about 6 microns indiameter or of about 6 microns per edge in a square shape, on thephoton-absorbing layer of the optical shutter.

In one embodiment, wherein the reverse reaction is induced by radiationselected from the group consisting of ultraviolet radiation, visibleradiation, and infrared radiation, a second modulator may be interposedbetween the source of the radiation and the optical shutter to provide adesired length of imaging time and a desired imagewise area for thereverse reaction of the optical shutter by the radiation. Suitablemodulators for the photon-induced reverse reaction may be any of thevariety of light modulators, such as electro-optic modulators, known inthe art of light modulators, depending on the requirements for the“on-off” imaging, such as described above for the first modulator, andof the desired imagewise area, such as a dot or pixel shape of about 6microns in diameter or of about 6 microns per edge in a square shape, onthe photon-absorbing layer of the optical shutter. In one embodiment,the wavelength of the photons to form the reaction product is differentfrom the wavelength of the radiation inducing the reverse reaction.

In one embodiment, the source of the photons is an electroluminescentlight-emitting device, as known in the art of inorganic and organicelectroluminescent LEDs. In one embodiment, the light-emitting devicehas a plurality of light-emitting pixels having a circumference and anintermittent light emission to provide a desired length of imaging time,such as 1.5 picoseconds of “on” time with 20 nanoseconds of “off” timeand a desired imagewise area, such as, for example, a dot or a pixelshape of about 6 microns in diameter or of about 6 microns per edge in asquare shape, for the imaging of the optical shutter by the photons. Inone embodiment, wherein the reverse reaction is induced by radiationselected from the group consisting of ultraviolet radiation, visibleradiation, and infrared radiation, a second electroluminescentlight-emitting device with a plurality of light-emitting pixels having acircumference and an intermittent light emission provides a desiredlength of imaging time, such as 1.5 picoseconds of “on” time and 60nanoseconds of “off” time, and a desired imagewise area, such as, forexample, a dot or a pixel shape of about 6 microns in diameter or ofabout 6 microns per edge in a square shape, for the reverse reaction ofthe optical shutter by the radiation. In one embodiment, the wavelengthof the photons to form the reaction product is different from thewavelength of the radiation inducing the reverse reaction

The organic radical cation may be a variety of salts of an aminiumradical cation. The choice of the counteranion for the salt depends on avariety of factors such as, for example, the desired speed of thephoto-induced reaction to form the reaction product, the desired speedof the reverse reaction of the reaction product to regenerate thestarting organic free radical compound, and the required stability ofthe photon-absorbing layer against degradation by oxygen, moisture, andthe photon exposures and reverse reactions during the operation of thereversible optical shutter.

For example, an anthrasemiquinone radical anion is a type ofcounteranion to use with an aminium radical cation, such as an IR-165type aminium radical cation, since the anthrasemiquinone radical anionis an electron-donating material which may participate by being oxidizedin the photon-induced reduction of the aminium radical cation and alsomay participate in the reverse reaction of the reaction product toregenerate the starting aminium radical cation by a simultaneous reversereduction to reform the anthrasemiquinone radical anion, particularlywhen the reverse reaction is induced or sensitized by ultraviolet,visible, or infrared radiation absorbed by the oxidation product, suchas the corresponding anthraquinone, of the anthrasemiquinone radicalanion. By the proper selection of the type of anthrasemiquinone radicalanion derivative, the anthrasemiquinone radical anion of the combinedaminium radical cation-anthrasemiquinone radical anion salt may be theorganic free radical that absorbs the photons to form the reactionproduct having a change in absorption at the wavelength, and the aminiumradical cation may participate in promoting this photon-induced reactionand in promoting the reverse reaction to regenerate the startinganthrasemiquinone radical anion.

The wavelength at which the optical shutter has the states of low andhigh absorption may be varied depending on the product application bythe selection of the organic free radical compound and by the totalcomposition of the photon-absorbing layer. Suitable wavelengths include,but are not limited to, the range of 400 to 2000 nm. The wavelength maybe a single wavelength or a range of multiple wavelengths. In oneembodiment, the wavelength is a wavelength from 400 to 1000 nm. In oneembodiment, the wavelength is a wavelength from 1000 to 1400 nm. In oneembodiment, the wavelength is a wavelength from 1400 to 1600 nm,preferably 1520 to 1580 mm and more preferably 1500 to 1700 nm, forapplications in fiber optics communications channels. In one embodiment,the wavelength is the range of wavelengths mentioned above, such as 400to 2000 nm and 1500 to 1700 nm.

The levels of absorption of the states of low and high absorption may bevaried depending on the product application by the selection of the typeand amount of the free radical compound and by the total composition ofthe photon-absorbing layer. Typically, the change in absorption at thewavelength is the primary property and may be a range of values from,for example, 0.1 in optical density to greater than 3.0 in opticaldensity, depending on the product application. For example, for atypical application of an optical shutter in an optical switch array ina fiber optics communications channel, the optical density of the lowstate of absorption at the wavelength, such as 1620 nm, should be as lowas possible, such as less than 0.01 or completely transparent, and theoptical density of the high state of absorption at the wavelength shouldbe very high, such as 3.1 or greater, when measured through the path ofthe optical shutter that the optical signals are directed to travel, toprovide the contrast ratio of greater than 30 dB or of a factor greaterthan 1000.

In the example of the optical shutter with a photon-absorbing layercomprising IR-165 described above, the absorption of the photons imagesthe optical shutter from the first state of low absorption to the secondstate of high absorption. Depending on the requirements for the opticalshutter in the specific product application, it is readily possible tomodify the photon-absorbing layer so that the absorption of photonsimages the optical shutter from the second state of high absorption tothe first state of low absorption. For example, the photon-absorbinglayer may comprise IR-126 or a similar aminium radical cation and thephoton-absorbing layer may comprise an oxidative, electron-acceptingmatrix of polymers, counteranions, and other additives around theaminium radical cation. Upon imaging of this optical shutter by photons,for example, at 980 nm, the IR-126 type aminium radical cation forms areaction product, such as an one-electron oxidation product that is thesame or similar to IR-165. Prior to the absorption of photons, theoptical shutter has a state of high absorption, such as an opticaldensity of 3.1 due to the IR-126 or similar organic free radicalcompound, at a wavelength, such as 1620 nm. After the absorption ofphotons and the formation of the reaction product, the optical shutterhas a state of low absorption, such as an optical density of less than0.05 due to IR-165 or similar organic free radical compound, at thewavelength, such as 1620 nm. The reverse reaction of the opticalshutter, as described heretofore, regenerates the starting free radicalcompound, a IR-126 type radical cation, and returns the optical shutterto the state of high absorption at the wavelength, such as 1620 nm.Thus, this embodiment of the optical shutter of the present invention isalso characterized by being reversibly imageable between the first andsecond states of absorption at the wavelength.

In one embodiment of the optical shutters of this invention, thereaction product forms in less than 1 nanosecond after the absorption ofthe photons by the free radical compound, preferably forms in less than0.1 nanoseconds after the absorption of the photons, more preferablyforms in less than 0.01 nanoseconds after the absorption of the photons,and most preferably forms in less than 0.001 nanoseconds afterabsorption of photons by the free radical compound. The formation of thereaction product at speeds of less than 0.001 nanoseconds or 1picosecond is particularly advantageous for product applications infiber optics communications channels where nanosecond optical datapacket switching is desired.

Organic free radical compounds, such as aminium radical cations, areparticularly suitable for sub-picosecond speeds of forming the reactionproduct, particularly by an photon-induced electron transfer reactionwhere no covalent bond breaking is required. The fact that IR-165 has asub-picosecond conversion of photons to heat in certain types ofphoton-absorbing layers but still exhibits some reversible formation ofIR-126 or a similar compound or, alternatively, some reversibleformation of a blue, organic free radical oxidation product, illustratesthat the speed of formation of these reaction products is fast enough tocompete with the sub-picosecond photon-to-heat conversion. In fact, thismay reversibly occur to a significant extent with some heat formationduring the reverse reaction during the photon excitation of the IR-165containing layer when the photon excitation times are long, such asgreater than 3 picoseconds, especially since photon-induced electrontransfer reactions are known to occur in sub-picosecond times as fast as40 femtoseconds and to be reversible by dark reactions at speeds as fastas 2 to 3 picoseconds. An organic free radical compound where theexcited state is an excited state from the free radical ground state mayhave a rapid internal conversion from this excited state back to theground state with a concomitant production of heat in a time scale of aslow as 1 picosecond or less. In one example of this, an organic radicalcation compound absorbs photons in the presence of a thermochromiccompound, converts the absorbed photons to heat in less than 1nanosecond, and causes a change in absorption due to heat-inducedchanges in the thermochromic compound, as described in PCT InternationalPublication No. WO 98/54615, titled “Optical Shutter Device” andpublished Dec. 3, 1998, to Carlson. The present invention utilizes anorganic free radical compound which undergoes a photo-induced electrontransfer reaction which causes changes in absorption due to theoxidation or the reduction of the free radical compound. Thisphoto-induced electron transfer reaction may occur faster and withhigher efficiency than internal conversion of the absorbed photons toheat or, alternatively, may have a similar or slightly lower speed andefficiency than this internal conversion to heat so that both electrontransfer and heat formation processes occur. The composition of thephoton-absorbing layer may be varied to maximize the efficiency of theformation of the reaction product and to minimize direct photon-to-heatand photon-to-luminescence conversions with a target to approach aquantum efficiency of 100% or 1.0 for the conversion of each photonabsorbed to form a molecule of reaction product. This efficiency wouldbe advantageous in reducing the amount of photons which are needed forimaging of the optical shutter. The very intense absorptions of theorganic free radicals are advantageous in making photon-absorbing layerswith a high optical density at the wavelength of the photons used toform the reaction product, thus providing a high percent absorption ofthese incident photons.

In one embodiment of the optical shutters of this invention, thereaction product is an oxidation product of the free radical compound,such as, for example, an one-electron oxidation product or atwo-electron oxidation product. IR-126 as the free radical compound andIR-165 as the reaction product is an example of the reaction productbeing an one-electron oxidation product. In one embodiment, the reactionproduct is a reduction product of the free radical compound, such as,for example, an one-electron reduction product and a two-electronreduction product. IR-165 as the free radical compound and IR-126 as thereaction product is an example of the reaction product being anone-electron reduction product. IR-126 as the free radical compound andits corresponding non-free radical amine as the reaction product areanother example of the reaction product being an one-electron reductionproduct.

In addition to the organic free radical compound, the photon-absorbinglayer of the optical shutter of the present invention may comprise othermaterials to provide mechanical integrity to the layer and to optimizethe formation of the reaction product and the reverse reaction toregenerate the starting organic free radical. Suitable materials for thephoton-absorbing layer include, but are not limited to, organic polymerssuch as polycarbonate and cellulosic polymers; inorganic glasses, suchas a porous grade of silica glass as known in the art of inorganicglasses; and one or more inorganic xerogel layers, as known in the artof xerogel layers. Because of the small sizes possible for the opticalshutter of this invention, organic polymers and inorganic xerogel layersare preferred because, unlike inorganic glasses, they are known to bereadily fabricated in layers with thicknesses of less than 8 microns bycoating and other deposition processes known in the art of manufacturinglayers with thicknesses of 0.1 to 8 microns. The one or more inorganicxerogel layers typically have a nanoporous structure with average porediameters in the range of 0.5 to 300 nm, which may be utilizedadvantageously to be filled partly or completely with the organic freeradical compound and other materials, such as polymeric materials,electron-accepting compounds, and electron-donating compounds, toprovide a nanocomposite photon-absorbing layer.

The organic nature of the organic free radical compounds and of theoptical shutter of the present invention are advantageous for ease offabrication, such as by conventional methods of coating or plasticmolding, in comparison to inorganic glass materials typically used inall-optical or hybrid optical shutters and switches. Since only the areaof the photon-absorbing layer that receives photons is imaged and actsas an optical shutter, the optical shutter may be made for ease offabrication and possible extension of its product lifetime with aphoton-absorbing layer of greater thickness and surface area than isneeded. This excess photon-absorbing layer may be utilized later if theoriginal optical shutter has degraded and a new optical shutter isneeded by re-positioning the optical shutter to expose this excessphoton-absorbing layer as the optical shutter in the productapplication.

The unique properties of the optical shutter of the present inventionare adapted for use in a variety of optical components for fiber opticscommunications channels, such as, for example, for an optical switchdevice, an optical buffer, an optical router, and a tunable optical gainfilter.

The optical shutter of the present invention may be utilized in any ofthe optical switch devices known in the art of fiber opticscommunications channels where the optical switch devices utilize one ormore optical shutters, or optical gates as optical shutters are oftenreferred to in fiber optics applications, that operate by a reversibleimaging between states of low and high absorptions, including wherethere is also simultaneous reversible imaging between states of low andhigh reflectivity. Each of these types of reversible imaging of opticalshutters or optical gates have been described herein for the opticalshutter of this invention.

One aspect of the optical switch devices of this invention pertains toan optical switch device comprising one or more optical input paths, twoor more optical output paths, and one or more optical shutters, whichone or more optical shutters are imageable by photons and have a firststate of a low absorption at a wavelength and a second state of a highabsorption at the wavelength, at least one of the one or more opticalshutters comprising a photon-absorbing layer, wherein thephoton-absorbing layer comprises an organic free radical compound and ischaracterized by absorption of the photons by the free radical compoundto form a reaction product having a change in absorption at thewavelength and by a reverse reaction of the reaction product toregenerate the free radical compound; and wherein at least one of theone or more shutters is characterized by being reversibly imageablebetween the first and second states of absorption; and further whereinat least one of the one or more optical shutters further comprise asurface layer having a low reflectivity state at the wavelength, whereinthe at least one of the one or more optical shutters is characterized byabsorption of the photons to form a surface layer having a highreflectivity state and by a reverse reaction of the high reflectivitystate to regenerate the low reflectivity state of the surface layer; andwherein the at least one of the one or more optical shutters ischaracterized by being reversibly imageable between the low and highreflectivity states; and wherein the optical switch array ischaracterized by being capable of switching an optical signal of thewavelength entering the switch array from a first optical input path toexiting the switch device in a first or a second optical output path.

Still another aspect of this invention pertains to an optical switchdevice comprising one or more optical input paths, two or more opticaloutput paths, and one or more optical shutters, the one or more shuttershaving a first state of transparency and of low reflectivity at a rangeof wavelengths and a second state of opacity and of high reflectivity atthe range of wavelengths, and at least one of the one or more shutterscomprising a first surface layer in a transparent state, a secondsurface layer in a transparent state, and a photon-absorbing layer in atransparent state and interposed between the first and second surfacelayers, wherein the at least one of the one or more optical shutters, asdescribed herein, that comprise the photon-absorbing and surface layers,is characterized by absorption of photons to change at least one of thefirst and second surface layers to a state of high reflectivity and tochange the photon-absorbing layer to a state of opacity, and further ischaracterized by being reversibly imageable between the first and secondstates; and wherein the switch device is characterized by being capableof switching an optical signal entering the switch device from one ofthe one or more input paths to a selected one of the two or more outputpaths.

In one embodiment, the at least one of the one or more optical shutterscomprising the photon-absorbing and surface layers comprises ametallized layer on at least one side of the photon-absorbing layer. Inone embodiment, the metallized layer comprises aluminum. In oneembodiment, the photon-absorbing layer comprises an organic free radicalcompound and is characterized by an absorption of photons to form areaction product having a change in absorption at the range ofwavelengths.

In one embodiment of the optical switch devices of the presentinvention, the reversible imaging from the second state to the firststate occurs with no external source of energy. In one embodiment, thereversible imaging from the second state to the first state is inducedby heat. In one embodiment, the reversible imaging from the second stateto the first state is induced by absorption of photons from one or morewavelength ranges selected from the group consisting of ultravioletwavelength ranges, visible wavelength ranges, and infrared wavelengthranges. In one embodiment, the first and second surface layers are indirect contact to the photon-absorbing layer. In one embodiment, the atleast one of the first and second surface layers is not in directcontact to the photon-absorbing layer. In one embodiment, the at leastone of the one or more shutter comprises two or more photon-absorbinglayers interposed between the first and second surface layers. In oneembodiment, the first surface layer is in direct contact to a first oneof the two or more photon-absorbing layers and the second surface layeris in direct contact to a second one of the two or more photo-absorbinglayers.

In one embodiment, the absorption of the photons images the at least oneof the one or more optical shutters from the first state of lowabsorption to the second state of high absorption, thereby insuring thatno optical signal is transmitted through the photon-absorbing layerwhile the optical signal is simultaneously reflected from the surfacelayer having a high reflectivity state. Referring to FIG. 1, oneembodiment of an optical switch device 110 utilizing the opticalshutters of this invention having reversible imaging between both lowand high absorption states of a photon-absorbing layer and between lowand high reflectivity states of a surface layer, is illustrated. A firstinput path 1 having an input optical signal 1(IN) at the wavelength,such as, for example, 1620 nm, of the specific communication channeldirects the input optical signal 1(IN) to a reflective surface 15, suchas a mirror. The reflective surface 15 then directs the input opticalsignal 1(IN) at an optical shutter 14 comprising a surface layer 9having a low reflectivity state and a photon-absorbing layer 7comprising an organic free radical compound or other photon-absorbingcompound, such as a non-free radical compound that forms an organic freeradical compound by an electron transfer. When the photon-absorbinglayer 7 of optical shutter 14 absorbs photons from a light source suchas a light source above or below the plane of the optical path of theoptical signals in FIG. 1, the organic free radical compound or otherphoton-absorbing compound absorbs the photons and forms a reactionproduct providing a change from a state of low absorption to a state ofhigh absorption at 1620 nm, such as, for example, a decrease in opticaldensity at 1620 nm from 3.10 to 0.03 in the optical path of the opticalswitch that the optical signals are directed to travel. Simultaneouslythe surface layer 9 of optical shutter 14 is imaged from the lowreflectivity state to a second state of high reflectivity. While thereaction product is formed and the optical density and the reflectivityat 1620 nm are very high, this optical signal is reflected to areflective surface 25, such as a mirror. The optical signal is thenreflected by reflective surface 25 to a second output path 2 where theoptical signal becomes an output optical signal 2(OUT) at 1620 nm.Alternatively, instead of a reflective surface 25, the change indirection of the optical signal may be done by bends in a waveguidecarrying the optical signal or by other direction-changing opticalcomponents known in the art of fiber optics communications channels.Prior to any absorption of photons by optical shutter 14 or when thereaction product and the surface layer with the high reflectivity stateundergo the reverse reaction to regenerate the starting organic freeradical compound or other photon-absorbing compound and to regeneratethe surface layer with a low reflectivity state, the optical density andthe reflectivity at 1620 nm are very low, and the optical signal canpass through optical shutter 14 and optical shutter 16 to output path 1where the optical signal becomes an output optical signal 1(OUT) at 1620nm.

Similarly, a second input path 2 having an input optical signal 2(IN) atthe wavelength, such as, for example, 1620 nm, of the specificcommunications channel directs the input optical signal at an opticalshutter 16 comprising a surface layer 9 having a low reflectivity stateand a photon-absorbing layer 7 comprising an organic free radicalcompound or other photon-absorbing compound. When the photon-absorbinglayer 7 of optical shutter 16 absorbs photons from a light source suchas a light source above or below the plane of the optical signals inFIG. 1, the organic free radical compound or other photon-absorbingcompound absorbs the photons and forms a reaction product providing achange from a state of low absorption to a state of high absorption at1620 nm and simultaneously the surface layer 9 of optical shutter 16 isimaged from the low reflectivity state to a second state of highreflectivity. While the reaction product is formed and the opticaldensity and the reflectivity at 1620 nm are very high, this opticalsignal is reflected to output path 1 where the optical signal becomes anoutput optical signal 1(OUT) at 1620 nm. Prior to any absorption ofphotons by optical shutter 16 or when the reaction product and thesurface layer with the high reflectivity state undergo the reversereaction to regenerate the starting organic free radical or otherphoton-absorbing compound and to regenerate the surface layer with a lowreflectivity state, the optical density and the reflectivity at 1620 nmare very low, and the optical signal can pass through optical shutter 16and optical shutter 14 to the reflective surface 25. The optical signalis then reflected by reflective surface 25 to the second output path 2where the optical signal becomes an output optical signal 2(OUT) at 1620nm.

Optical shutter 16 and optical shutter 14 are in close proximity andform an optical shutter in the configuration of a double optical shutterassembly 18, but the light sources to image the optical shutters may becollimated and focused to provide photons that image only a singleoptical shutter in the optical switch device, such as only imagingoptical shutter 16 without imaging optical shutter 14 of double opticalshutter assembly 18.

Many variations and combinations of the optical shutters of the presentinvention with their flexibility to be “transparent-to-opaque” opticalshutters, “opaque-to-transparent” optical shutters,“transparent-to-reflective” optical shutters, and“reflective-to-transparent” optical shutters, as described herein, maybe utilized in the designs of the optical switch devices of thisinvention, including use in optical switch devices known in the artwhere the designs require “transparent-to-opaque” opaque shutters,“opaque-to-transparent” optical shutters, “transparent-to-reflective”optical shutters, and “reflective-to-transparent” optical shutters.

Referring to FIG. 2 where the numbers and words have the same meaning asused for these same symbols in FIG. 1, in another embodiment of theoptical switch devices of the present invention, an optical combiningdevice 30 is placed after the double optical shutter assembly 18 tocombine and collect the optical signals that have either reflected fromfixed mirror 15 or from optical shutter 16, as well as any other opticalsignals also directed to the combining device 30 at the same time, andto direct these optical signals to output path 1. Similarly, an opticalcombining device 32 is placed after fixed mirror 25 to combine andcollect the optical signals that have reflected from fixed mirror 25either after passing through double optical shutter assembly 18 in itstransparent state or after reflecting off optical shutter 14 of doubleoptical shutter assembly 18 in a reflective state and to direct thesesignals to output path 2. Optical combining devices, as known in the artof devices for combining optical signals that are on different paths anddirections but are in close proximity, are useful with the opticalshutter, such as the double optical shutter assemblies, and the opticalswitch devices of this invention to collect optical signals which may beon slightly different optical paths depending on the switching pathbeing utilized and combining and connecting these optical signals in anefficient manner to the desired output path.

Referring to FIG. 3, in another embodiment of the optical shutters ofthis invention, the optical shutter 101 has a single photon-absorbinglayer 105 interposed between two surface layers 102 and 103. Thephoton-absorbing layer 105 is in a transparent state when the twosurface layers 102 and 103 are in a transparent state to provide theoptical shutter 101 in a transparent state. In the reflective state ofthe optical shutter, the photon-absorbing layer 105 is in an opaquestate and the two surfaces 102 and 103 are in a reflective state. Asillustrated in FIG. 3, the optical signals are provided to and from theoptical shutter 101 through waveguides. Two waveguides 51 and 52, whoseinternal width where the optical signals are present, is represented byw, intersect at an angle θ with respect to the input paths of theincoming optical signals. In FIG. 3, θ is 90° and in general, 0<θ<180°.The width of the photon-absorbing layer 105 in the optical shutter 101is denoted as a. The optical shutter 101 is positioned at an angle ofθ/2 with respect to the input paths of the incoming optical signals andwith its centerline 104 over points A and B of intersection ofwaveguides 51 and 52.

When the optical shutter 101 is in the transparent state, an opticalsignal C that is entering the 2×2 optical switch device on the firstinput path 110 will pass through the optical shutter 101 and exit on thefirst output path 111. Similarly, an optical signal D that is enteringthe 2×2 optical switch device on the second input path 112 will passthrough the optical shutter 101 and exit on the second output path 113.In contrast, when the optical shutter 101 is in the reflective state, anoptical signal C that is entering the 2×2 optical switch device on thefirst input path 110 will be reflected at surface layer 102 and exit onthe second output path 113, and optical signal D that is entering the2×2 optical switch device on the second input path 112 will be reflectedat surface layer 103 and exit on the first output path 111.

Referring to FIG. 3 and considering the state when the optical shutter101 is in the reflective state on both surfaces, the path of opticalsignal C when reflected at surface layer 102 into the second output path113 is shifted relative to the path of optical signal D when the latterexits on the second output path 113 when the optical shutter 101 is inthe transparent state. The tapered regions 120 and 121 are useful toefficiently collect the optical signals after they have passed throughthe optical shutter 101 and to funnel them to a waveguide region of adesired reduced width, such as, for example, the width w of the inputwaveguides.

A wide variety of shapes are suitable for the tapered region, with FIG.3 disclosing one alternative. For example, the wider width of thetapered region compared to the width of the input waveguide may be onone side of the output waveguide after the optical signal exits thereflecting surface layer, as for example illustrated in FIG. 3, or itmay be divided between both sides of the output waveguide after theoptical signal exits the reflecting surface layer, such as, for example,symmetrically divided between both sides. This preferred configurationof the tapered region will be dependent on the position of the opticalshutter 101 in the intersection of the two input paths and the twooutput paths. For example, the minimum width f of the widest width ofthe tapered region in the section of the output waveguide that isadjacent to the reflective surface layer is the distance between pointsE and B and equivalently between points B and F in FIG. 3. The minimumwidth f depends on w, a, and 0 by the relationship shown in equation(1):

f=w+[a•cos(θ/2)]  (1)

For the sake of simplicity, the energy source that causes the opticalshutter to change its state from transparent to reflective or fromreflective to transparent in the 2×2 optical switch array of FIG. 3 isnot shown. This energy source may be above and/or below the plane of theoptical switch device as this plane is illustrated in the top down viewof FIG. 3. In one embodiment, the optical signal travels in a waveguidein the one or more input paths and in a selected one of the two or moreoutput paths immediately prior to and immediately after the opticalsignal reaches the at least one of said one or more shutters comprisingthe photon-absorbing and surface layers. In one embodiment, thewaveguide in the two or more output paths is tapered from a largerdimension in contact to at least one of the first and second surfacelayers to a smaller dimension at a distance from the at least one of thefirst and second surface layers.

Referring to FIG. 4, the numbers and letters have the same meaning asused for these same symbols in FIG. 3. FIG. 4 illustrates one embodimentof a 2×2 optical switch device comprising an optical shutter of thepresent invention where the optical signals travel into and from theoptical shutter in a free space configuration rather than in a waveguideconfiguration. To efficiently collect the optical signal from thereflective surface layers as well as when the optical shutter is in atransparent state, the tapered regions of the waveguide mode asillustrated in FIG. 3, are replaced with lenses 44 with a suitablecurvature to shape and focus the output optical signal to a desiredshape. This shape is typically less in size than the shape representedby the optical signals as they would exit the optical shutter in anoutput path from both the reflective and transparent states. In oneembodiment, the optical signal travels in free space in the one or moreinput paths and in a selected one of the two or more output pathsimmediately prior to and immediately after the optical signal reachesthe at least one of the one or more shutters comprising thephoton-absorbing and surface layers. In one embodiment, the switchdevice comprises a lens in the two or more output paths to focus theoptical signal.

Referring to FIGS. 5A and 5B, one embodiment of a 2×2 optical switchdevice of the present invention is illustrated. For the sake ofsimplicity, the optical shutter as illustrated in FIGS. 1 to 4, isillustrated in FIGS. 5A and 5B as a single line and, instead of awaveguide mode or a free space mode, only the path of the input andoutput optical signals is indicated by lines with arrows on each segmentof the line to indicate the paths which could involve either a waveguidemode or a free space mode in the optical shutters and optical switchdevices of the present invention.

In FIG. 5A in a top down view, the optical shutter 10 is in thetransparent state 11. The optical signal on the first input path 1reflects from mirror 15 and is directed to pass through the transparentoptical shutter 10 and to exit the 2×2 optical switch device on thefirst output path 3. The optical signal on the second input path 2passes through the transparent optical shutter 10, reflects from mirror25, and is directed to exit the 2×2 optical switch device on the secondoutput path 4.

In FIG. 5B in a top down view, the optical shutter 10 is in thereflective state 22. The optical signal on the first input path 1reflects from mirror 15, is directed to the reflective optical shutterwhere it is reflected and directed to mirror 25, then reflects frommirror 25, and is directed to exit the 2×2 optical switch device on thesecond output path 4. The optical signal on the second input path 2reflects from the reflective optical shutter 10 and is directed to exitthe 2×2 optical switch device on the first output path 3.

Referring to FIG. 6 (not to scale), one embodiment of an energy sourcein combination with an optical shutter is illustrated for use in theoptical shutters and optical switch devices of this invention. Anoptical shutter 101 (not to scale) is shown in a perspective view fromone side. The optical shutter 101 has a first surface layer 102, asecond opposite surface layer 104, and a photon-absorbing layer 103interposed between the two surface layers. Above the optical shutter101, there is a source 1 of photons 2 which can provide photons of thedesired wavelengths and intensities to cause the optical shutter 101 tochange from a transparent to a reflective state or from a reflective toa transparent state. Where photons of different wavelengths are desiredto reverse the change of the optical shutter, source 1 may be tunabledirectly or by the indirect use of filters to provide these photons ofdifferent wavelengths or, alternatively, a second source of photons maybe positioned below or positioned above in a different exposure path tothe optical shutter to cause the reverse photon-induced change in theoptical shutter. More than one source of photons may be positioned toprovide the desired photolytic exposure of the optical shutter for theforward and for the reverse changes of the optical shutter. For the sakeof simplicity, lenses, such as, for example, aspheric lenses, and otheroptical components known in the art of photolytic imaging for focusing abeam of photons on the desired imagewise area, are not shown in FIG. 6.Also, as shown in FIG. 6, an optical switch control circuit device isconnected to the source of photons. The optical switch control circuitdevice monitors the desired timing for providing the photons anddelivers a signal to the source of photons to provide the photons to theat least one of the one or more optical shutters comprising thephoton-absorbing and surface layers. Instead of photons, suitablesources of energy to switch the optical shutters and switch devices ofthis invention include, but are not limited to, electrical currentsource elements and heating sources elements. In one embodiment, theoptical switch devices comprises one or more external energy sourceelements to provide energy to switch the optical shutter comprising thephoton-absorbing and surface layers; wherein the one or more externalenergy source elements are selected from the group consisting ofelectrical current source elements, heating source elements, ultravioletsource elements, visible light source elements, and infrared radiationsource elements. In one embodiment, the one or more external energysource elements are connected to an optical switch control circuitdevice that monitors the desired timing for providing the energy anddelivers a signal to the one or more external sources of energy toprovide the energy to the at least one of the one or more opticalshutters comprising the photon-absorbing and surface layers.

A wide variety of optical switch device designs are possible utilizingthe reversible transparent-to-reflective optical shutters of the presentinvention. For example, optical switch devices where the number of inputpaths for the optical signals is represented by M and the number ofoutput paths for the optical signals is represented by N, where M may ormay not be equal to N, may be implemented from the interconnection of2×2 optical switches, as known in the art of M×N optical switch devicesand arrays. For example, the cross-bar is a known design wherein theswitching component, such as the reversible transparent-to-reflectiveoptical shutters of the present invention, may be arranged in arectangular array of dimensions M×N. When an optical signal enters onany one of the M input paths, it may exit on any one of the N outputpaths depending on the state of the optical shutters in the switchdevice. For example, FIG. 7 illustrates a 4×4 optical cross-bar switchdevice having 16 optical shutters represented by a circle only for theoptical shutters in the transparent state, wherein each optical shutterhas a transparent-to-reflective surface positioned at an angle to theinput optical signal such that, in the reflective state of the opticalshutter, the input optical signal is directed to a specific output path.As an illustration of one possible state of this 4×4 cross-bar, opticalshutters 102 are in the reflective state as also indicated by a diagonalline through the circle, and the other 12 optical shutters are in thetransparent state. In such a configuration, an optical signal thatenters on input path 1 will exit on output path 3. Similarly, opticalsignals entering on input paths 2, 3, and 4 will exit on output paths 1,2, and 4, respectively. By changing the state of this 4×4 cross-bar tohave other combinations of 4 optical shutters in the reflective state,optical signals on any one of the 4 input paths may exit from any one ofthe four output paths.

As illustrated, for example, in FIG. 7, one aspect of the presentinvention pertains to an optical cross-bar switch device, comprising (a)an array of optical shutters arranged in a plurality of columns androws, each optical shutter having a first state of transparency and oflow reflectivity in a range of wavelengths and a second state of opacityand of high reflectivity in the range of wavelengths, the shuttercomprising a first surface layer in a transparent state, a secondsurface layer in a transparent state, and a photon-absorbing layer in atransparent state and interposed between the first and second layers,wherein the optical shutter is characterized by the absorption ofphotons to change at least one of the first and second surface layers toa state of high reflectivity and to change the photon-absorbing layer toa state of opacity; wherein the optical shutter is characterized bybeing reversibly imageable between the first and second states; and (b)a plurality of fiber optic ports, each fiber optic port disposed at arespective one of the columns and rows and capable of emitting andreceiving a light beam so that when the light beam from a light emittingfiber optic port located at a selected one of the columns and rows istransmitted to a selected light receiving fiber optic port located at aselected remaining one of the columns and rows, the optical shutterlocated at an intersection formed by the selected column and row isswitched to change from the non-reflective state to the reflective stateto reflect the light beam from the light emitting fiber optic port tothe selected light receiving fiber optic port. In one embodiment, theswitch device further comprises a plurality of collimator elements, eachcollimator element being disposed adjacent to respective ones of eachfiber optic port and between each fiber optic port and the opticalshutters. In one embodiment, when the optical shutter located at theintersection formed by the selected column and row is in the secondstate, remaining ones of the optical shutters located in the selectedcolumn and row are in the first state, as illustrated, for example, inFIG. 7. In one embodiment, a plurality of light beams from a pluralityof light emitting fiber optic ports located at selected ones of thecolumns and rows are transmitted to a plurality of selected lightreceiving fiber optic ports located at selected remaining ones of therows and columns through a plurality of optical shutters located atrespective intersections formed by the selected columns and rows in therespective reflective states, as illustrated, for example, in FIG. 7. Inone embodiment, when the plurality of rows are oriented parallel to eachother, the plurality of columns are oriented parallel to each other, andthe plurality of rows and columns are oriented perpendicularly relativeto each other, as illustrated, for example, in FIG. 7.

A special case of the cross-bar switch device is the 1×N switch, where acommon application is to switch an optical signal to one of N alternatepaths, each path having a distinct attribute or function, and then thealternate paths may be recombined at an optical combining device. FIG. 8illustrates one embodiment of a 1×N switch array where N is four and theoutput paths for the optical signals are positioned parallel to theinput path. The switching function is implemented with three opticalshutters, each represented by a circle and having atransparent-to-reflective surface. Optical shutter 101 has itsreflective surface layer, as represented by a diagonal line, facing tothe lower left side of the figure, while optical shutters 102 and 103have reflecting surface layers, represented by diagonal lines, facing tothe upper right. A permanent reflecting surface 104, such as a mirror,is used so that all four alternate output paths are parallel to oneanother. For example, an optical signal entering on input path 105 willexit on output path 106 if optical shutters 101 and 103 are in thereflective state and optical shutter 102 is in the transparent state.

The 2×2 optical switch device of FIGS. 1, 2, 5A, and 5 may be readilyexpanded to larger switch devices, such as, for example, to 1280×1280optical switch devices where there may be, for example, 16 opticalfibers carrying optical signals with each fiber having 80 differentwavelengths, such as 80 wavelengths ranging from 1530 to 1620 nm. The“transparent-to-reflective” type of optical shutter illustrated in FIGS.1, 2, 5A, and 5B with its optical shutter assembly of either two opticalshutters in close proximity or a single optical shutter comprising aphoton-absorbing layer interposed between two surface layers, may havean overall size as small as, for example, about 8 microns per edge of acubic shape. If the optical switch device operates by having the 16incoming fibers of each specific wavelength be demultiplexed and inputto the optical switch device in a single plane with the 16 fiberscarrying the other 79 specific wavelengths being likewise successivelypositioned and provided with demultiplexed signals in 79 individualplanes parallel and above or below this first plane and further operatesby having the optical shutters of each plane is offset enough from theoptical shutters of any other plane that the source of light from aboveor below the 80 planes of the optical switch device may image a singleindividual optical shutter without imaging any other optical shutters,the optical switch device may have a very compact size. For example,assuming a 8 micron length per edge of a cubic shape for double opticalshutter assembly 18 in FIG. 1, the dimensions of a corresponding1280×1280 optical switch device based on this type of“transparent-to-reflective” optical shutter and double optical shutterassembly may be estimated to be as small as about 8 microns multipliedby 16 fibers or 128 microns in one dimension in a single plane of 16optical signals, about 8 microns multiplied by 80 wavelengths or 640microns in depth to account for the total of 80 planes for each of theindividual wavelengths, and about 8 microns multiplied by 80 wavelengthsand then multiplied by 16 signals or 10,240 microns in the seconddimension in each single plane carrying optical signals to account forthe offsetting to provide the ability to image only a single opticalshutter without imaging any other optical shutters. This extremely smallsize is very advantageous for cost, ease of manufacturing, and spaceconsiderations for both optical switch devices and for the light sourcesto image the optical switch devices.

Referring to FIG. 9, one embodiment of a 16×16 optical switch device 100of the present invention is illustrated. As described above, this 16×16optical switch device could be just one plane of a 3-dimensional opticalswitch device of a larger size, such as up to 1280×1280 and larger M×Ndevices, where different optical switch devices are on planes parallelto each other and offset relative to the source of photons to switch theoptical shutter so that the source of photons from above and/or belowthe planes carrying the optical signals may expose and switch onlyspecific optical shutters, as desired. FIG. 9 is a top down view that issimilar to the smaller optical switch devices shown in FIGS. 1, 2, 5A,and 5B. Input optical signals are represented by the vertical lines justabove the numbers 0 through 15 on the bottom side of the optical switchdevice triangle where it is labeled IN and before any intersections withhorizontal lines. Output optical signals are represented by thehorizontal lines just to the left of the numbers 0 through 15 on theright side of the optical switch device triangle where it is labeled OUTand before any intersections with vertical lines. The dashed lines101-116 are reflecting surfaces, such as mirrors. Each intersection ofcontinuous horizontal and vertical lines represents a double opticalswitch assembly configuration of the optical shutters of the presentinvention, as described herein. Similar to the functioning as describedfor FIGS. 1, 2, 5A, and 5B, for example, an optical signal entering oninput path 3 may be switched to output path 11 by switching the opticalshutter at the intersection 1103 of the vertical line extending frominput path 11 and the horizontal line extending from output path 3. Thisreflects the optical signal at the intersection 1103 to reflectingsurface 111, where it is again reflected to exit on output path 11.Similarly, the input optical signals on any one of the input paths maybe switched to exit on any one of the output paths.

Since the optical switch devices, such as 2×2 optical switch devices,may be used in conjunction with other components, including other 2×2optical switch devices, an important feature is the convenientinterconnection of the optical components in the case of opticalswitching devices in both waveguide and free space configurations. Theoptical switch devices of this invention may have a wide variety ofalternative configurations where the input paths and the output pathsfor the optical signals have various orientations with respect to eachother. For example, in FIGS. 1 and 2, the two input paths for theoptical signals are parallel to each other, and the two output paths forthe optical signals are parallel to each other and at right angles tothe input paths. The optical shutters of this invention provideexcellent flexibility for alternative orientations of the input and theoutput paths. For example, if it is desired to position two inputoptical paths such that when the optical shutter is in the transparentstate, the two optical signals cross one another at an angle θ wherethis angle is determined with respect to the incoming paths, and whenthe optical shutter is in the reflective state, it is desired that theoptical signals switch positions on the output optical paths, this maybe obtained if the double optical shutter assembly configuration of theoptical shutter is positioned with the reflecting surface on the opticalinput side at an angle of one half of θ to the input optical path.

For example, referring to FIG. 10 in a top down view similar to that inFIGS. 5A and 5B with the double optical shutter assembly configurationof the optical shutter represented as a single line, the input path 1for the first optical signal 101 is at an acute angle to the input path2 for the second optical signal 102. θ in this case is 60° so one halfof θ is 30°. For the reflective state of the optical shutter 103, thepath taken by the first optical signal 101 is represented by a dashedline, and the path taken by the second optical signal 102 is representedby a solid line. The output paths for both of these optical signals isat an angle of one half of θ or 30° with respect to the plane of thereflecting surfaces of the optical shutter 103.

FIG. 11 further illustrates the flexibility of the orientation of theinput and output optical paths with the optical shutters and switchdevices of the present invention. In this case, the input paths for thetwo optical signals 101 and 102 are at right angles to each other. θ isthus 90°, and one half of θ is 45°. As with FIG. 10, in FIG. 11, for thereflective state of the optical shutter 103, the path taken by the firstoptical signal 101 is represented by a dashed line, and the path takenby the second optical signal 102 is represented by a solid line. Theoutput paths for both of these optical signals is at an angle of onehalf of θ or 45° with respect to the plane of the reflecting surfaces ofthe optical shutter 103.

FIG. 12 provides another illustration of the flexibility of theorientation of the input and output optical paths with the opticalshutters and switch devices of this invention. In this case, the inputpaths for the two optical signals 101 and 102 are at an angle of 150° toeach other, and one half of θ is 75°. As with FIGS. 10 and 11, for thereflective state of the optical shutter 103, the path taken by the firstoptical signal 101 is represented by a dashed line, and the path takenby the second optical signal 102 is represented by a solid line.Accordingly, the output paths for both of these optical signals is at anangle of one half of θ or 75° with respect to the plane of thereflecting surfaces of the optical shutter 103.

In one embodiment of the optical switch devices of the presentinvention, the reaction product formed in the photon-absorbing layer isthe free radical compound. In one embodiment, the absorption of photonsimages the at least one of the one or more optical shutters comprisingthe photon-absorbing and surface layers from the second state to thefirst state, and preferably, the reaction product is formed from thefree radical compound. In one embodiment, the free radical compound is asalt of an aminium radical cation. In a preferred embodiment, the freeradical compound is a salt of atetrakis[4-(dialkylamino)phenyl]-1,4-benzenediamine radical cation. In apreferred embodiment, the free radical compound is a salt of aN,N-dialkyl-N′,N′-bis[4-(dialkylamino)phenyl]-1,4-benzenediamine radicalcation. In one embodiment, the free radical compound is a salt of ananthrasemiquinone radical anion. In one embodiment, the wavelength rangeof the photons to form the reaction product comprises one or moreultraviolet wavelengths. In one embodiment, the wavelength range of thephotons to form the reaction product comprises one or more wavelengthsfrom 400 to 700 nm. In one embodiment, the wavelength range of thephotons to form the reaction product comprises one or more wavelengthsfrom 700 to 2000 nm.

In one embodiment of the optical switch devices of this invention, thereversible imaging between the first and second states is induced byabsorption of photons, and wherein the wavelength range of photonsimaging the optical shutter from the first state to the second state isdifferent from the wavelength range of photons imaging the opticalshutter from the second state to the first state. In one embodiment, therange of wavelengths where the switching goes between the first andsecond states is from 400 to 2000 nm. In one embodiment, the range ofwavelengths is from 1000 to 1700 nm. In one embodiment, the range ofwavelengths is from 1400 to 1700 nm. In one embodiment, the range ofwavelengths is from 1500 to 1700 nm.

In one embodiment of the optical switch devices of the presentinvention, an optical combining device is present in at least one of thetwo or more output paths to direct the optical signal to the selectedone of the two or more output paths. In one embodiment, a first fixedmirror is present in the one of the one or more input paths and a secondfixed mirror is present in the one of the two or more output paths whenthe optical signal is switched between the optical input and outputpaths in the switch device.

In one embodiment of the optical switch devices of this invention, theoptical signal is reflected from the at least one of the first andsecond surfaces at an angle from 10 and 89°, as illustrated, forexample, in FIGS. 10, 11, and 12. In one embodiment, the optical signalis reflected from the at least one of the first and second surfaces atan angle of 45°, as illustrated, for example, in FIG. 11.

In one embodiment of the optical switch devices of the presentinvention, the number of the optical input paths is from 2 to 1280, thenumber of the optical output paths is from 2 to 1280, and the number ofthe optical shutters comprising the photon-absorbing and surface layersis from 1 to 9600. In one embodiment, the optical switch device isconnected to optical input paths or to optical output paths of one ormore other optical switch devices. In one embodiment, the second surfacelayer is reflective so that a different optical signal can be reflectedwhile the first surface layer is reflecting the optical signal. In thiscase, for example, the optical shutters of the present invention mayalso switch optical signals traveling in opposite directions in the sameoptical input paths and optical output paths. In one embodiment, opticalsignals in the one or more optical input paths and the two or moreoptical output paths are bi-directional, and the optical switch deviceis characterized by the ability to switch the optical signals travelingin opposite directions through the optical switch device.

In one embodiment of the optical shutters and switch devices of thisinvention, the optical shutters may comprise three or more surfacelayers in a transparent state and a photon-absorbing layer in atransparent state and interposed between each of the three or moresurface layers. For example, the optical shutter could be cubic in shapeand have 6 surface layers with the photon-absorbing layer between eachof the 6 surface layers or have 3 to 5 only of the sides of thecubic-shaped optical shutter that are surface layers that reversiblyimage between a transparent state and a reflective state while thephoton-absorbing layer reversibly images between a transparent state andan opaque state. These optical shutters and switch devices with three ormore transparent-to-reflective surface layers may be useful in certainapplications requiring a more complex geometry for the paths of theoptical signals.

In one embodiment of the optical switch devices of this invention, theoptical switch device further comprises an optical wavelength conversionelement to convert the optical signal at the wavelength, such as 1542nm, to a second different wavelength, such as 1544 nm. This providesadditional flexibility in switching the optical signals to other outputpaths, such as to other available wavelengths in the same or differentoptical fiber. For example, the addition of one or more opticalwavelength conversion elements could convert the eighty 16×16 opticalswitch devices described in connection with FIG. 9 into a 1280×1280optical switch device, where any input optical signal may be switched toany one of the 1280 possible output paths for the output opticalsignals. Preferred are optical wavelength conversion elements which arecapable of converting the optical signal to a different wavelength thatis one, two, or three wavelengths above or below the wavelength of theinput optical signal. Stable organic free radical compounds typicallyhave large molecular structures in order to stabilize the free radicalmoiety. As such, they typically have large molecular cross-sections,very high absorption extinction coefficients, and often sub-picosecondspeed conversions of photons absorbed to heat, to electron transferreactions, and to luminescence. Accordingly, these organic free radicalcompounds may be modified to provide non-linear optical properties thatalter the frequency of the photons passing through a layer comprisingthe organic free radical compound and thereby provide a wavelengthconversion to the photons. In one embodiment, the optical wavelengthconversion layer comprises an organic free radical compound. In oneembodiment, the switch device further comprises an optical wavelengthconversion element to convert the optical signal having a firstwavelength to an optical signal of a second different wavelength. In oneembodiment, the optical wavelength conversion element comprises anorganic free radical compound as an active material for converting thewavelength of the optical signal having the first wavelength.

Methods of Switching Optical Signals

As described herein, the optical shutters and switch devices of thepresent invention provide a variety of methods for switching an opticalsignal from an optical input path to a selected optical output path.

One aspect of this invention pertains to a method for switching anoptical signal from one optical input path to a predetermined one of aplurality of different optical output paths, which method comprises thesteps of (a) providing a free-space optical switch device, comprising anoptical shutter disposed between an optical input path and a first andsecond optical output paths, the optical shutter being switchablebetween a transparent state in which the light from the input path istransmitted through the optical shutter to the first output path, and areflective state in which the light from the input path is reflectedfrom the optical shutter to the second output path; (b) inputting anoptical signal into the input path; and (c) providing photons to switchthe optical shutter reversibly between the transparent state and thereflective state in order to selectively direct the optical signal to apredetermined one of the output paths. In one embodiment, the opticalshutter comprises a first surface layer in a transparent state, a secondsurface layer in a transparent state, and a photon-absorbing layer in atransparent state and interposed between the first and second surfacelayers, wherein the optical shutter is characterized by the absorptionof photons to change at least one of the first and second surface layersto a state of high reflectivity and to change the photon-absorbing layerto a state of opacity; and wherein the optical shutter is characterizedby being reversibly imageable between the first and second states. Inone embodiment, the photon-absorbing layer comprises an organic freeradical compound in at least one of the first and second states.

Another aspect of this invention pertains to a method for switching anoptical signal from one optical input path to a predetermined one of aplurality of different optical output paths, which method comprises thesteps of (a) providing a optical switch device, comprising an opticalshutter disposed between an optical input port in a first inputwaveguide and both a first optical output port in a first waveguide anda second optical output port in a second output waveguide, the opticalshutter being switchable between a transparent state in which the lightfrom the input port is transmitted through the optical shutter to saidfirst output port, and a reflective state in which the light from theinput port is reflected from said optical shutter to said second outputport; (b) inputting an optical signal into the input port; and (c)providing photons to switch the optical shutter reversibly between thetransparent state and the reflective state in order to selectivelydirect the optical signal to a predetermined one of the output ports. Inone embodiment, the optical shutter comprises a first surface layer in atransparent state, a second surface layer in a transparent state, and aphoton-absorbing layer in a transparent state and interposed between thefirst and second surface layers, wherein the optical shutter ischaracterized by the absorption of photons to change at least one of thefirst and second surface layers to a state of high reflectivity and tochange the photon-absorbing layer to a state of opacity; and wherein theoptical shutter is characterized by being reversibly imageable betweenthe first and second states. In one embodiment, the photon-absorbinglayer comprises an organic free radical compound in at least one offirst and second states.

Another aspect of the present invention pertains to a method forswitching an optical signal from one or more optical input paths to apredetermined one of two or more optical output paths, which methodcomprises the steps of (a) providing an optical switch device, asdescribed herein; (b) inputting an optical signal into the one or moreinput paths; and (c) providing photons to switch the optical shutterfrom the first state and the second state in order to selectively directthe optical signal to a predetermined one of the two or more outputpaths.

Optical Buffers

The optical shutters of the present invention may be utilized to preparean optical buffer to store optical signals for a specified delay timebefore sending the optical signals on to their next destination in theoptical network system. As the bit rates and the quantities of opticalsignals increase, a situation known generally as data contention, asknown in the art of fiber optics communication channels, becomes moreprevalent. This is especially a technical challenge as the fiber opticscommunication channels evolve to nanosecond optical burst switching andnanosecond optical packet switching. Data contention involves, forexample, two different packets of optical signals being in contention atthe same time for transmission to their next destination in the opticalnetwork. To resolve this contention, one of the packets of opticalsignals may be delayed in its transmission, such as, for example, bybeing placed into a fiber delay line where the speed of light (about 0.3mm per picosecond) may be used to provide the specified delay time.These fiber delay lines are expensive, complex, space-consuming, andrelatively inflexible to making variations in the desired delay time.These disadvantages may be overcome by utilizing the optical shutters ofthe present invention in an optical buffer.

Referring to FIG. 13, in one embodiment of an optical buffer, utilizingthe optical shutters of this invention having reversible imaging betweenboth low and high absorption states of a photon-absorbing layer andbetween low and high reflectivity states of a surface layer of thisinvention, is illustrated. An optical signal 1 at a wavelength, such as,for example, 1620 nm, or at multiple wavelengths, such as, for example,80 wavelengths in the range of 1530 to 1620 nm, is directed to anoptical network destination 110, such as, for example, an optical switchdevice for network optical core switching or an optical amplifier or anelectro-optic switch array for network edge switching, as described forexample in “Architectural and Technological Issues for Future OpticalInternet Networks,” in IEEE Communications Magazine, September 2000,pages 82 to 92, and references therein, by Listanti et al., thedisclosures of which are fully incorporated herein by reference. Opticalsignal 1 must pass through optical shutters 10 and 11 of optical buffer120 prior to continuing on to optical network destination 110. If a datacontention or other reason to delay the transmission of optical signal 1occurs, optical shutter 11 comprising a surface layer 9 of a lowreflectivity state and a photon-absorbing layer 7 is imaged, asdescribed previously for the similar optical shutters 14 and 16 in FIG.1. Optical signal 1 is then reflected to optical shutter 12 comprising asurface layer 9 of a low reflectivity state and a photon-absorbing layer7 and, if delay in optical buffer 120 is desired, optical shutter 12 isimaged, as described previously for the similar optical shutters 14 and16 in FIG. 1. Optical signal 1 is then reflected to optical shutter 13comprising a surface layer 9 of a low reflectivity state and aphoton-absorbing layer 7 and is imaged, as described previously for thesimilar type of optical shutters 14 and 16 in FIG. 1. Optical signal 1is then reflected to optical shutter 10 comprising a surface layer 9 ofa low reflectivity state and a photon-absorbing layer 7 and is imaged,as described previously for the similar type of optical shutters 14 and16 in FIG. 1. Optical signal 1 is then reflected to optical shutter 11,which by the time optical signal 1 has traveled around optical buffer120, has undergone the reverse reaction to regenerate the states of thelow absorption and the low reflectivity.

If no further delay is required, optical shutter 11 is not imaged, andoptical signal 1 continues on to optical network destination 110. Iffurther delay is required, optical shutter 11 is imaged, and opticalsignal 1 is reflected again to optical shutter 12 and the process ofstoring or delaying optical signal 1 in optical buffer 120 continuesuntil no further delay is required when optical signal 1 reaches opticalshutter 11. If only a single optical buffer is required, opticalshutters 12 and 13 do not need to be optical shutters and may bepermanent reflective surfaces, such as mirrors. At about 0.3 mm perpicosecond for the speed of light, the distance traveled by opticalsignal 1 in optical buffer 120 may be set to provide the desired delaytime in a single loop or in multiples of single loops around opticalbuffer 120. If the desired delay time varies and can not be met with asingle loop or any number of multiples of single loops, the distance fora single loop in optical buffer 120 may be adjusted by moving two ormore of the four optical shutters or mirrors to create a new distancefor a single loop or any number of multiple loops which matches the newdesired delay time.

If delay or optical signal storage in optical buffer 130 is desiredinstead, optical shutter 12 is not imaged, and optical signal 1continues on to optical buffer 130. Optical shutters 20, 21, 22, and 23have the same layers and alternative permanent reflective surfaces asherein described for optical shutters 10, 11, 12, and 13, respectively,in FIG. 13. Thus, it can be seen that optical signal 1 may be circulatedin a loop around optical buffer 130 by imaging the optical shutters andmay continue back to optical buffer 120 if optical shutter 20 is notimaged when optical signal 1 reaches optical shutter 20. When opticalsignal 1 is back in optical buffer 120, optical signal 1 may becirculated in a loop around optical buffer 120 by imaging the opticalshutters and may continue on to optical network destination 110 ifoptical shutter 11 is not imaged when optical signal 1 reaches opticalshutter 11. An optical buffer, such as optical buffer 130, that does nothave an optical shutter in the direct path of optical signal 1 tooptical network connection 110 is particularly advantageous to avoidadditional data contention by having the optical signals in the opticalbuffer, such as optical buffer 120, pass additional times through theinput optical path. Also, this is useful when the desired delay time islong, such as more than 10 nanoseconds.

Similar optical buffers may be provided in other locations adjacent tooptical buffers 120 and 130 in a manner similar to which optical buffers120 and 130 are adjacent to each other and may also be accessed byoptical signal 1. Also, the reflective surface of one or more opticalshutters in a first optical buffer may be angled such that the opticalsignal is reflected to a second optical buffer on a different plane.Similarly, the reflective surface of one or more optical shutters in thesecond or other optical buffer may be angled such that the opticalsignal is reflected back to the plane of the first optical buffer. Thiswould provide more flexibility in storing and retrieving the opticalsignals from a number of optical buffers of the present invention.Additional optical buffers would provide additional buffering capacityand additional flexibility in handling a variety of optical data packetswhich may have a wide range of byte sizes from, for example, 50 bytes to1500 bytes and thus may have varying desired delay times which are notall integer multiples of each other. As one alternative to additionaloptical buffers connected optically to a first optical buffer, a singleoptical buffer may have more than two optical shutters on each edge ofthe optical buffer, such as, for example, 100 optical shutters oppositeto each other on each edge instead of the two optical shutters oppositeto each other on each edge in optical buffers 120 and 130, so that thedelay time may be readily changed by the choice of which of the opticalshutters to image when the optical signal reaches the specific opticalshutter.

Thus, one aspect of the optical buffers of this invention pertains to anoptical buffer for storing an optical signal for a desired time, whichoptical buffer comprises at least two optical shutters positioned atfirst distances and first angles from each other, wherein the at leasttwo optical shutters are imageable by photons and have a first state ofa low absorption at a wavelength and a second state of a high absorptionat the wavelength, which optical shutters comprise a photon-absorbinglayer, wherein the photon-absorbing layer comprises an organic freeradical compound and is characterized by absorption of the photons bythe free radical compound to form a reaction product having a change inabsorption at the wavelength and by a reverse reaction of the reactionproduct to regenerate the free radical compound; and wherein the atleast two optical shutters are characterized by being reversiblyimageable between the first and second states of absorption; and the atleast two optical shutters further comprise a surface layer having a lowreflectivity state at the wavelength, wherein the at least two opticalshutters are characterized by absorption of said photons to form asurface layer having a high reflectivity state and by a reverse reactionof the high reflectivity state to regenerate the low reflectivity state,wherein the at least two optical shutters are characterized by beingreversibly imageable between the low and high reflectivity states; andwherein at least two of the at least two optical shutters are interposedbetween an input path carrying the optical signal and an output path forthe optical signal.

In one embodiment of the optical buffers of this invention, theabsorption of the photons images the optical shutter from the firststate of low absorption to the second state of high absorption. In oneembodiment, the optical buffer further comprises two or more reflectivesurfaces, such as, for example, two or more “transparent-to-reflective”optical shutters or two mirrors, positioned at second distances andsecond angles from the at least two optical shutters to return theoptical signal to at least one of the at least two optical shutters. Inone embodiment, the first distances, first angles, second distances, andsecond angles are selected to return the optical signal in the desiredtime to one of the at least two optical shutters interposed between theinput channel and the output channel. In one embodiment, the firstdistances, first angles, second distances, and second angles areadjustable to match changes in the desired time for storing the opticalsignal.

In the optical buffers of the present invention, the photon-absorbinglayers of the optical shutter preferably comprise an organic freeradical compound, but other materials that induce a reversible“transparent-to-opaque” imaging of the photon-absorbing layer may beutilized.

While the invention has been described in detail and with reference tospecific and general embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

What is claimed is:
 1. An optical switch device, said switch devicecomprising one or more optical input paths, two or more optical outputpaths, and one or more optical shutters, said one or more shuttershaving a first state of transparency and of low reflectivity at a rangeof wavelengths and a second state of opacity and of high reflectivity atsaid range of wavelengths, and at least one of said one or more shutterscomprising a photon-absorbing layer and a surface layer on at least oneside of said photon-absorbing layer, wherein said photon-absorbing layercomprises an organic free radical compound in at least one of said firstand second states and is characterized by absorption of photons to forma reaction product having a change in absorption at said range ofwavelengths; and wherein said at least one of said one or more shutterscomprising said photon-absorbing and surface layers is characterized bybeing reversibly imageable between said first and second states; andwherein said switch device is characterized by being capable ofswitching an optical signal entering said switch device from one of saidone or more input paths to a selected one of said two or more outputpaths.
 2. The optical switch device of claim 1, wherein said at leastone of said one or more shutters comprising said photon-absorbing andsurface layers comprises a metallized layer on at least one side of saidphoton-absorbing layer.
 3. The optical switch device of claim 2, whereinsaid metallized layer comprises aluminum.
 4. The optical switch deviceof claim 1, wherein said absorption of photons images said at least oneof said one or more shutters comprising said photon-absorbing andsurface layers from said first state to said second state.
 5. Theoptical switch device of claim 4, wherein said reaction product is saidfree radical compound.
 6. The optical switch device of claim 1, whereinsaid absorption of photons images said at least one of said one or moreshutters comprising said photon-absorbing and surface layers from saidsecond state to said first state.
 7. The optical switch device of claim6, wherein said reaction product is formed from said free radicalcompound.
 8. The optical switch device of claim 1, wherein absorption ofphotons reversibly images said at least one of said one or more shutterscomprising said photon-absorbing and surface layers between said firstand second states.
 9. The optical switch device of claim 8, wherein thewavelength range of photons imaging said at least one of said one ormore shutters comprising said photon-absorbing and surface layers fromsaid first state to said second state is different from the wavelengthrange of photons for reversibly imaging from said second state to saidfirst state.
 10. The optical switch device of claim 1, wherein saidreaction product is formed from said free radical compound.
 11. Theoptical switch device of claim 1, wherein said reaction product is saidfree radical compound.
 12. The optical switch device of claim 1, whereinsaid free radical compound is a salt of an aminium radical cation. 13.The optical switch device of claim 1, wherein said free radical compoundis a salt of a tetrakis[4-(dialkylamino)phenyl]-1,4-benzenediamineradical cation.
 14. The optical switch device of claim 1, wherein saidfree radical compound is a salt of aN,N-dialkyl-N′,N′-bis[4-(dialkylamino)phenyl]-1,4-benzenediamine radicalcation.
 15. The optical switch device of claim 1, wherein said freeradical compound is a salt of an anthrasemiquinone radical anion. 16.The optical switch device of claim 1, wherein the wavelength range ofsaid photons to form said reaction product comprises one or moreultraviolet wavelengths.
 17. The optical switch device of claim 1,wherein the wavelength range of said photons to form said reactionproduct comprises one or more wavelengths from 400 to 700 nm.
 18. Theoptical switch device of claim 1, wherein the wavelength range of saidphotons to form said reaction product comprises one or more wavelengthsfrom 700 to 2000 nm.
 19. The optical switch device of claim 1, whereinsaid range of wavelengths is from 400 to 2000 nm.
 20. The optical switchdevice of claim 1, wherein said range of wavelengths is from 1000 to1700 nm.
 21. The optical switch device of claim 1, wherein said range ofwavelengths is from 1400 to 1700 nm.
 22. The optical switch device ofclaim 1, wherein said range of wavelengths is from 1500 to 1700 nm. 23.The optical switch device of claim 1, wherein said switch device furthercomprises an optical wavelength conversion element to convert saidoptical signal having a first wavelength to an optical signal of asecond different wavelength.
 24. The optical switch device of claim 23,wherein said optical wavelength conversion element comprises an organicfree radical compound as an active material for converting thewavelength of said optical signal having a first wavelength.
 25. Anoptical switch device, said switch device comprising one or more opticalinput paths, two or more optical output paths, and one or more opticalshutters, said one or more shutters having a first state of transparencyand of low reflectivity at a range of wavelengths and a second state ofopacity and of high reflectivity at said range of wavelengths, and atleast one of said one or more shutters comprising a first surface layerin a transparent state, a second surface layer in a transparent state,and a photon-absorbing layer in a transparent state and interposedbetween said first and second surface layers, wherein said at least oneof said one or more shutters comprising said photon-absorbing andsurface layers is characterized by absorption of photons to change atleast one of said first and second surface layers to a state of highreflectivity and to change said photon-absorbing layer to a state ofopacity, and further is characterized by being reversibly imageablebetween said first and second states; and wherein said switch device ischaracterized by being capable of switching an optical signal enteringsaid switch device from one of said one or more input paths to aselected one of said two or more output paths.
 26. The optical switchdevice of claim 25, wherein said at least one of said one or moreoptical shutters comprising said photon-absorbing and surface layers ischaracterized by the absorption of photons to change both of said firstand second surface layers to a state of high reflectivity.
 27. Theoptical switch device of claim 26, wherein the changes in reflectivityof said first and second surface layers occur reversibly at the sametime.
 28. The optical switch device of claim 25, wherein said at leastone of said one or more optical shutters comprising saidphoton-absorbing and surface layers comprises a metallized layer on atleast one side of said photon-absorbing layer.
 29. The optical switchdevice of claim 28, wherein said metallized layer comprises aluminum.30. The optical switch device of claim 25, wherein the reversibleimaging from said second state to said first state occurs with noexternal source of energy.
 31. The optical switch device of claim 25,wherein the reversible imaging from said second state to said firststate is induced by heat.
 32. The optical switch device of claim 25,wherein the reversible imaging from said second state to said firststate is induced by absorption of photons from one or more wavelengthranges selected from the group consisting of ultraviolet wavelengthranges, visible wavelength ranges, and infrared wavelength ranges. 33.The optical switch device of claim 25, wherein said first and secondsurface layers are in direct contact to said photon-absorbing layer. 34.The optical switch device of claim 25, wherein at least one of saidfirst and second surface layers is not in direct contact to saidphoton-absorbing layer.
 35. The optical switch device of claim 25,wherein said at least one of said one or more shutters comprising saidphoton-absorbing and surface layers comprises two or morephoton-absorbing layers interposed between said first and second surfacelayers.
 36. The optical switch device of claim 35, wherein said firstsurface layer is in direct contact to a first one of said two or morephoton-absorbing layers and said second surface layer is in directcontact to a second one of said two or more photon-absorbing layers. 37.The optical switch device of claim 25, wherein said photon-absorbinglayer comprises an organic free radical compound and is characterized byan absorption of photons to form a reaction product having a change inabsorption at said range of wavelengths.
 38. The optical switch deviceof claim 37, wherein said reaction product is said free radicalcompound.
 39. The optical switch device of claim 37, wherein saidabsorption of photons images said at least one of said one or moreshutters comprising said photon-absorbing and surface layers from saidsecond state to said first state.
 40. The optical switch device of claim39, wherein said reaction product is formed from said free radicalcompound.
 41. The optical switch device of claim 37, wherein said freeradical compound is a salt of an aminium radical cation.
 42. The opticalswitch device of claim 37, wherein said free radical compound is a saltof a tetrakis[4-(dialkylamino)phenyl]-1,4-benzenediamine radical cation.43. The optical switch device of claim 37, wherein said free radicalcompound is a salt of aN,N-dialkyl-N′,N′-bis[4-(dialkylamino)phenyl]-1,4-benzenediamine radicalcation.
 44. The optical switch device of claim 37, wherein said freeradical compound is a salt of an anthrasemiquinone radical anion. 45.The optical switch device of claim 37, wherein the wavelength range ofsaid photons to form said reaction product comprises one or moreultraviolet wavelengths.
 46. The optical switch device of claim 37,wherein the wavelength range of said photons to form said reactionproduct comprises one or more wavelengths from 400 to 700 nm.
 47. Theoptical switch device of claim 37, wherein the wavelength range of saidphotons to form said reaction product comprises one or more wavelengthsfrom 700 to 2000 nm.
 48. The optical switch device of claim 25, whereinreversible imaging between said first and second states is induced byabsorption of photons, and wherein the wavelength range of photonsimaging said shutter from said first state to said second state isdifferent from the wavelength range of photons imaging said shutter fromsaid second state to said first state.
 49. The optical switch device ofclaim 25, wherein said range of wavelengths is from 400 to 2000 nm. 50.The optical switch device of claim 25, wherein said range of wavelengthsis from 1000 to 1700 nm.
 51. The optical switch device of claim 25,wherein said range of wavelengths is from 1400 to 1700 nm.
 52. Theoptical switch device of claim 25, wherein said range of wavelengths isfrom 1500 to 1700 nm.
 53. The optical switch device of claim 25, whereinan optical combining device is present in at least one of said two ormore output paths to direct said optical signal to a selected one ofsaid two or more output paths.
 54. The optical switch device of claim25, wherein a first fixed mirror is present in said one of said one ormore input paths and a second fixed mirror is present in said selectedone of said two or more output paths when said optical signal isswitched between the input and output paths in said switch device. 55.The optical switch device of claim 25, wherein said optical signal isreflected from said at least one of said first and second surface layersat an angle from 1° and 89°.
 56. The optical switch device of claim 25,wherein said optical signal is reflected from said at least one of saidfirst and second surface layers at an angle of 45°.
 57. The opticalswitch device of claim 25, wherein the number of said one or more inputpaths is from 2 to 1280, the number of said two or more output paths isfrom 2 to 1280, and the number of said optical shutters comprising saidphoton-absorbing and surface layers is from 1 to
 9600. 58. The opticalswitch device of claim 25, wherein said switch device is connected to anoptical input path or to an optical output path of one or more otheroptical switch devices.
 59. The optical switch device of claim 25,wherein said second surface layer is reflective in said second state sothat a different optical signal can be reflected when said first surfacelayer is reflecting said optical signal.
 60. The optical switch deviceof claim 25, wherein optical signals in said one or more input paths andsaid two or more output paths are bi-directional, and said switch deviceis characterized by the ability to switch optical signals traveling inopposite directions through said switch device.
 61. The optical switchdevice of claim 25, wherein said switch device comprises one or moreexternal energy source elements to provide energy to switch said opticalshutter comprising said photon-absorbing and surface layers; whereinsaid one or more external energy source elements are selected from thegroup consisting of electrical current source elements, heating sourceelements, ultraviolet light source elements, visible light sourceelements, and infrared radiation source elements.
 62. The optical switchdevice of claim 61, wherein said one or more external energy sourceelements are connected to an optical switch control circuit device thatmonitors the desired timing for providing said energy and delivers asignal to said one or more external sources of energy to provide saidenergy to said at least one of said one or more shutters comprising saidphoton-absorbing and surface layers.
 63. The optical switch device ofclaim 25, wherein said optical signal travels in free space in said oneor more input paths and in a selected one of said two or more outputpaths immediately prior to and immediately after said optical signalreaches said at least one of said one or more shutters comprising saidphoton-absorbing and surface layers.
 64. The optical switch device ofclaim 63, wherein said switch device comprises a lens in said two ormore output paths to focus said optical signal.
 65. The optical switchdevice of claim 25, wherein said optical signal travels in a waveguidein said one or more input paths and in a selected one of said two ormore output paths immediately prior to and immediately after saidoptical signal reaches said at least one of said one or more shutterscomprising said photon-absorbing and surface layers.
 66. The opticalswitch device of claim 65, wherein said waveguide in said two or moreoutput paths is tapered from a larger dimension in contact to at leastone of said first and second surface layers to a smaller dimension at adistance from said at least one of said first and second surface layers.67. An optical cross-bar switch device, comprising: (a) an array ofoptical shutters arranged in a plurality of columns and rows, eachoptical shutter having a first state of transparency and of lowreflectivity in a range of wavelengths and a second state of opacity andof high reflectivity in said range of wavelengths, said shuttercomprising a first surface layer in a transparent state, a secondsurface layer in a transparent state, and a photon-absorbing layer in atransparent state and interposed between said first and second layers,wherein said optical shutter is characterized by the absorption ofphotons to change at least one of said first and second surface layersto a state of high reflectivity and to change said photon-absorbinglayer to a state of opacity; wherein said optical shutter ischaracterized by being reversibly imageable between said first andsecond states; and (b) a plurality of fiber optic ports, each fiberoptic port disposed at a respective one of the columns and rows andcapable of emitting and receiving a light beam so that when the lightbeam from a light emitting fiber optic port located at a selected one ofthe columns and rows is transmitted to a selected light receiving fiberoptic port located at a selected remaining one of the columns and rows,the optical shutter located at an intersection formed by the selectedcolumn and row is switched to change from the non-reflective state tothe reflective state to reflect the light beam from the light emittingfiber optic port to the selected light receiving fiber optic port. 68.The optical cross-bar switch device of claim 67, wherein said switchdevice further comprises a plurality of collimator elements, eachcollimator element being disposed adjacent to respective ones of eachfiber optic port and between each fiber optic port and the opticalshutters.
 69. The optical cross-bar switch device of claim 67, whereinwhen the optical shutter located at the intersection formed by theselected column and row is in said second state, remaining ones of theoptical shutters located in the selected column and row are in saidfirst state.
 70. The optical cross-bar switch device of claim 69,wherein a plurality of light beams from a plurality of light emittingfiber optic ports located at selected ones of the columns and rows aretransmitted to a plurality of selected light receiving fiber optic portslocated at selected remaining ones of the rows and columns through aplurality of optical shutters located at respective intersections formedby the selected columns and rows in the respective second states. 71.The optical cross-bar switch device of claim 67, wherein the pluralityof rows are oriented parallel to each other, the plurality of columnsare oriented parallel to each other, and the plurality of rows andcolumns are oriented perpendicularly relative to each other.